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href="#Dictionaries"> <div class="vector-toc-text"> 1.9.2 Dictionaries </div> </a> <ul id="toc-Dictionaries-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Maps" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Maps"> <div class="vector-toc-text"> 1.9.3 Maps </div> </a> <ul id="toc-Maps-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-F#" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#F#"> <div class="vector-toc-text"> 1.10 F# </div> </a> <ul id="toc-F#-sublist" class="vector-toc-list"> <li id="toc-Map<'Key,'Value>" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Map<'Key,'Value>"> <div class="vector-toc-text"> 1.10.1 Map<'Key,'Value> </div> </a> <ul id="toc-Map<'Key,'Value>-sublist" class="vector-toc-list"> <li id="toc-Creation_2" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Creation_2"> <div class="vector-toc-text"> 1.10.1.1 Creation </div> </a> <ul id="toc-Creation_2-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Access_by_key_2" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Access_by_key_2"> <div class="vector-toc-text"> 1.10.1.2 Access by key </div> </a> <ul id="toc-Access_by_key_2-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Dictionary<'TKey,'TValue>" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Dictionary<'TKey,'TValue>"> <div class="vector-toc-text"> 1.10.2 Dictionary<'TKey,'TValue> </div> </a> <ul id="toc-Dictionary<'TKey,'TValue>-sublist" class="vector-toc-list"> <li id="toc-Creation_3" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Creation_3"> <div class="vector-toc-text"> 1.10.2.1 Creation </div> </a> <ul id="toc-Creation_3-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Access_by_key_3" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Access_by_key_3"> <div class="vector-toc-text"> 1.10.2.2 Access by key </div> </a> <ul id="toc-Access_by_key_3-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Enumeration_2" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Enumeration_2"> <div class="vector-toc-text"> 1.10.3 Enumeration </div> </a> <ul id="toc-Enumeration_2-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-FoxPro" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#FoxPro"> <div class="vector-toc-text"> 1.11 FoxPro </div> </a> <ul id="toc-FoxPro-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Go" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Go"> <div class="vector-toc-text"> 1.12 Go </div> </a> <ul id="toc-Go-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Haskell" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Haskell"> <div class="vector-toc-text"> 1.13 Haskell </div> </a> <ul id="toc-Haskell-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Java" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Java"> <div class="vector-toc-text"> 1.14 Java </div> </a> <ul id="toc-Java-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-JavaScript" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#JavaScript"> <div class="vector-toc-text"> 1.15 JavaScript </div> </a> <ul id="toc-JavaScript-sublist" class="vector-toc-list"> <li id="toc-Map_and_WeakMap" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Map_and_WeakMap"> <div class="vector-toc-text"> 1.15.1 Map and WeakMap </div> </a> <ul id="toc-Map_and_WeakMap-sublist" class="vector-toc-list"> <li id="toc-Creation_4" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Creation_4"> <div class="vector-toc-text"> 1.15.1.1 Creation </div> </a> <ul id="toc-Creation_4-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Access_by_key_4" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Access_by_key_4"> <div class="vector-toc-text"> 1.15.1.2 Access by key </div> </a> <ul id="toc-Access_by_key_4-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Enumeration_3" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Enumeration_3"> <div class="vector-toc-text"> 1.15.1.3 Enumeration </div> </a> <ul id="toc-Enumeration_3-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Object" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Object"> <div class="vector-toc-text"> 1.15.2 Object </div> </a> <ul id="toc-Object-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Julia" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Julia"> <div class="vector-toc-text"> 1.16 Julia </div> </a> <ul id="toc-Julia-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-KornShell_93,_and_compliant_shells" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#KornShell_93,_and_compliant_shells"> <div class="vector-toc-text"> 1.17 KornShell 93, and compliant shells </div> </a> <ul id="toc-KornShell_93,_and_compliant_shells-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Lisp" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Lisp"> <div class="vector-toc-text"> 1.18 Lisp </div> </a> <ul id="toc-Lisp-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-LPC" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#LPC"> <div class="vector-toc-text"> 1.19 LPC </div> </a> <ul id="toc-LPC-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Lua" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Lua"> <div class="vector-toc-text"> 1.20 Lua </div> </a> <ul id="toc-Lua-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Mathematica_and_Wolfram_Language" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Mathematica_and_Wolfram_Language"> <div class="vector-toc-text"> 1.21 Mathematica and Wolfram Language </div> </a> <ul id="toc-Mathematica_and_Wolfram_Language-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-MUMPS" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#MUMPS"> <div class="vector-toc-text"> 1.22 MUMPS </div> </a> <ul id="toc-MUMPS-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Objective-C_(Cocoa/GNUstep)" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Objective-C_(Cocoa/GNUstep)"> <div class="vector-toc-text"> 1.23 Objective-C (Cocoa/GNUstep) </div> </a> <ul id="toc-Objective-C_(Cocoa/GNUstep)-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-OCaml" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#OCaml"> <div class="vector-toc-text"> 1.24 OCaml </div> </a> <ul id="toc-OCaml-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-OptimJ" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#OptimJ"> <div class="vector-toc-text"> 1.25 OptimJ </div> </a> <ul id="toc-OptimJ-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Perl_5" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Perl_5"> <div class="vector-toc-text"> 1.26 Perl 5 </div> </a> <ul id="toc-Perl_5-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Perl_6_(Raku)" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Perl_6_(Raku)"> <div class="vector-toc-text"> 1.27 Perl 6 (Raku) </div> </a> <ul id="toc-Perl_6_(Raku)-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-PHP" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#PHP"> <div class="vector-toc-text"> 1.28 PHP </div> </a> <ul id="toc-PHP-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Pike" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Pike"> <div class="vector-toc-text"> 1.29 Pike </div> </a> <ul id="toc-Pike-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-PostScript" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#PostScript"> <div class="vector-toc-text"> 1.30 PostScript </div> </a> <ul id="toc-PostScript-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Prolog" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Prolog"> <div class="vector-toc-text"> 1.31 Prolog </div> </a> <ul id="toc-Prolog-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Python" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Python"> <div class="vector-toc-text"> 1.32 Python </div> </a> <ul id="toc-Python-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Red" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Red"> <div class="vector-toc-text"> 1.33 Red </div> </a> <ul id="toc-Red-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-REXX" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#REXX"> <div class="vector-toc-text"> 1.34 REXX </div> </a> <ul id="toc-REXX-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Ruby" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Ruby"> <div class="vector-toc-text"> 1.35 Ruby </div> </a> <ul id="toc-Ruby-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Rust" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Rust"> <div class="vector-toc-text"> 1.36 Rust </div> </a> <ul id="toc-Rust-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-S-Lang" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#S-Lang"> <div class="vector-toc-text"> 1.37 S-Lang </div> </a> <ul id="toc-S-Lang-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Scala" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Scala"> <div class="vector-toc-text"> 1.38 Scala </div> </a> <ul id="toc-Scala-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Smalltalk" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Smalltalk"> <div class="vector-toc-text"> 1.39 Smalltalk </div> </a> <ul id="toc-Smalltalk-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-SNOBOL" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#SNOBOL"> <div class="vector-toc-text"> 1.40 SNOBOL </div> </a> <ul id="toc-SNOBOL-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Standard_ML" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Standard_ML"> <div class="vector-toc-text"> 1.41 Standard ML </div> </a> <ul id="toc-Standard_ML-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Tcl" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Tcl"> <div class="vector-toc-text"> 1.42 Tcl </div> </a> <ul id="toc-Tcl-sublist" class="vector-toc-list"> <li id="toc-array" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#array"> <div class="vector-toc-text"> 1.42.1 array </div> </a> <ul id="toc-array-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-dict" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#dict"> <div class="vector-toc-text"> 1.42.2 dict </div> </a> <ul id="toc-dict-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Visual_Basic" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Visual_Basic"> <div class="vector-toc-text"> 1.43 Visual Basic </div> </a> <ul id="toc-Visual_Basic-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Visual_Basic_.NET" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Visual_Basic_.NET"> <div class="vector-toc-text"> 1.44 Visual Basic .NET </div> </a> <ul id="toc-Visual_Basic_.NET-sublist" class="vector-toc-list"> <li id="toc-Creation_5" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Creation_5"> <div class="vector-toc-text"> 1.44.1 Creation </div> </a> <ul id="toc-Creation_5-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Access_by_key_5" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Access_by_key_5"> <div class="vector-toc-text"> 1.44.2 Access by key </div> </a> <ul id="toc-Access_by_key_5-sublist" 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.sidebar-title-with-pretitle{background:transparent!important}html.skin-theme-clientpref-night .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle a{color:var(--color-progressive)!important}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-list-title,html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle{background:transparent!important}html.skin-theme-clientpref-os .mw-parser-output .sidebar:not(.notheme) .sidebar-title-with-pretitle a{color:var(--color-progressive)!important}}@media print{body.ns-0 .mw-parser-output .sidebar{display:none!important}}</style><table class="sidebar nomobile nowraplinks" style="width:115px"><tbody><tr><th class="sidebar-title"><a href="/wiki/Comparison_of_programming_languages" title="Comparison of programming languages">Comparison of programming languages</a></th></tr><tr><td class="sidebar-content" style="text-align: left"> <ul><li><a href="/wiki/Comparison_of_programming_languages" title="Comparison of programming languages">General comparison</a></li> <li><a href="/wiki/Assignment_(computer_science)#Notation" title="Assignment (computer science)">Assignment</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(syntax)" title="Comparison of programming languages (syntax)">Basic syntax</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(basic_instructions)" title="Comparison of programming languages (basic instructions)">Basic instructions</a></li> <li><a href="/wiki/Comment_(computer_programming)#Comparison" title="Comment (computer programming)">Comments</a></li> <li>Control flow <ul><li><a href="/wiki/Foreach_loop#Language_support" title="Foreach loop">Foreach loops</a></li> <li><a href="/wiki/While_loop#Demonstrating_while_loops" title="While loop">While loops</a></li> <li><a href="/wiki/For_loop#Timeline_of_the_for-loop_syntax_in_various_programming_languages" title="For loop">For loops</a></li> <li><a href="/wiki/Do_while_loop#Demonstrating_do_while_loops" title="Do while loop">Do-while</a></li></ul></li> <li><a href="/wiki/Exception_handling_syntax" title="Exception handling syntax">Exception handling</a></li> <li><a href="/wiki/Enumerated_type#Syntax_in_several_programming_languages" title="Enumerated type">Enumerated types</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(algebraic_data_type)" title="Comparison of programming languages (algebraic data type)">Algebraic data types</a></li> <li><a href="/wiki/Generator_(computer_programming)#Timeline" title="Generator (computer programming)">Generators</a></li> <li><a href="/wiki/Anonymous_function#Examples" title="Anonymous function">Anonymous functions</a></li> <li><a href="/wiki/Ternary_conditional_operator" title="Ternary conditional operator">Conditional expressions</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(functional_instructions)" class="mw-redirect" title="Comparison of programming languages (functional instructions)">Functional instructions</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(array)" title="Comparison of programming languages (array)">Arrays</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(associative_arrays)" class="mw-redirect" title="Comparison of programming languages (associative arrays)">Associative arrays</a></li> <li><a href="/wiki/Scope_(computer_science)#By_language" title="Scope (computer science)">Scope</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(strings)" title="Comparison of programming languages (strings)">String operations</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(string_functions)" title="Comparison of programming languages (string functions)">String functions</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(higher-order_functions)" class="mw-redirect" title="Comparison of programming languages (higher-order functions)">Higher-order functions</a> <ul><li><a href="/wiki/Filter_(higher-order_function)#Language_comparison" title="Filter (higher-order function)">Filter</a></li> <li><a href="/wiki/Fold_(higher-order_function)#In_various_languages" title="Fold (higher-order function)">Fold</a></li> <li><a href="/wiki/Map_(higher-order_function)#Language_comparison" title="Map (higher-order function)">Map</a></li></ul></li> <li><a href="/wiki/Comparison_of_programming_languages_by_type_system" title="Comparison of programming languages by type system">Type systems</a> <ul><li><a href="/wiki/Comparison_of_programming_languages_with_dependent_types" class="mw-redirect" title="Comparison of programming languages with dependent types">Dependent types</a></li></ul></li> <li><a href="/wiki/Comparison_of_programming_languages_(list_comprehension)" title="Comparison of programming languages (list comprehension)">List comprehension</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(object-oriented_programming)" title="Comparison of programming languages (object-oriented programming)">Object-oriented programming</a></li> <li><a href="/wiki/Constructor_(object-oriented_programming)" title="Constructor (object-oriented programming)">Object-oriented constructors</a></li> <li><a href="/wiki/Comparison_of_programming_languages_(operators)" class="mw-redirect" title="Comparison of programming languages (operators)">Operators</a> <ul><li><a href="/wiki/Ternary_conditional_operator#Usage" title="Ternary conditional operator">Ternary conditional operator</a></li> <li><a href="/wiki/Null_coalescing_operator#Examples_by_languages" title="Null coalescing operator">Null coalescing operators</a></li> <li><a href="/wiki/Safe_navigation_operator#Examples" title="Safe navigation operator">Safe navigation operators</a></li> <li><a href="/wiki/Modulo_operation#In_programming_languages" class="mw-redirect" title="Modulo operation">Modulo operators</a></li></ul></li></ul></td> </tr><tr><td class="sidebar-content" style="text-align: left"> <ul><li><a href="/wiki/Evaluation_strategy" title="Evaluation strategy">Evaluation strategy</a></li> <li><a href="https://en.wikibooks.org/wiki/Computer_Programming/Hello_world" class="extiw" title="b:Computer Programming/Hello world">List of "Hello World" programs</a></li></ul></td> </tr><tr><td class="sidebar-content" style="text-align: left"> <hr /> <div class="collapsible-list mw-collapsible mw-collapsed" style="text-align: left;"> <div style="line-height: 1.6em; font-weight: bold;"><div>Comparison of individual languages</div></div> <ul class="mw-collapsible-content" style="margin-top: 0; margin-bottom: 0; line-height: inherit;"><li style="line-height: inherit; margin: 0">Comparison of Java and .NET platforms </li><li style="line-height: inherit; margin: 0"><a href="/wiki/ALGOL_58#ALGOL_58's_influence_on_ALGOL_60" title="ALGOL 58">ALGOL 58's influence on ALGOL 60</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/ALGOL_60#Comparisons_with_other_languages" title="ALGOL 60">ALGOL 60: Comparisons with other languages</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_ALGOL_68_and_C%2B%2B" title="Comparison of ALGOL 68 and C++">Comparison of ALGOL 68 and C++</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/ALGOL_68#Comparisons_with_other_languages" title="ALGOL 68">ALGOL 68: Comparisons with other languages</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Compatibility_of_C_and_C%2B%2B" title="Compatibility of C and C++">Compatibility of C and C++</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_Pascal_and_Delphi" title="Comparison of Pascal and Delphi">Comparison of Pascal and Borland Delphi</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_Object_Pascal_and_C" class="mw-redirect" title="Comparison of Object Pascal and C">Comparison of Object Pascal and C</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_Pascal_and_C" title="Comparison of Pascal and C">Comparison of Pascal and C</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_Java_and_C%2B%2B" title="Comparison of Java and C++">Comparison of Java and C++</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_C_Sharp_and_Java" title="Comparison of C Sharp and Java">Comparison of C# and Java</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_C_Sharp_and_Visual_Basic_.NET" title="Comparison of C Sharp and Visual Basic .NET">Comparison of C# and Visual Basic .NET</a> </li><li style="line-height: inherit; margin: 0"><a href="/wiki/Comparison_of_Visual_Basic_and_Visual_Basic_.NET" title="Comparison of Visual Basic and Visual Basic .NET">Comparison of Visual Basic and Visual Basic .NET</a> </li></ul> </div></td> </tr><tr><td class="sidebar-navbar"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Comparison_of_programming_languages" title="Template:Comparison of programming languages"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Comparison_of_programming_languages" title="Template talk:Comparison of programming languages"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Comparison_of_programming_languages" title="Special:EditPage/Template:Comparison of programming languages"><abbr title="Edit this template">e</abbr></a></li></ul></div></td></tr></tbody></table> <style data-mw-deduplicate="TemplateStyles:r886046785">.mw-parser-output .toclimit-2 .toclevel-1 ul,.mw-parser-output .toclimit-3 .toclevel-2 ul,.mw-parser-output .toclimit-4 .toclevel-3 ul,.mw-parser-output .toclimit-5 .toclevel-4 ul,.mw-parser-output .toclimit-6 .toclevel-5 ul,.mw-parser-output .toclimit-7 .toclevel-6 ul{display:none}</style><div class="toclimit-3"><meta property="mw:PageProp/toc" /></div> This comparison of programming languages (associative arrays) compares the features of <a href="/wiki/Associative_array" title="Associative array">associative array</a> <a href="/wiki/Data_structure" title="Data structure">data structures</a> or array-lookup processing for over 40 computer <a href="/wiki/Programming_language" title="Programming language">programming languages</a>. <div class="mw-heading mw-heading2"><h2 id="Language_support">Language support</h2>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=1" title="Edit section: Language support">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">This is a <a href="/wiki/Wikipedia:WikiProject_Lists#Dynamic_lists" title="Wikipedia:WikiProject Lists">dynamic list</a> and may never be able to satisfy particular standards for completeness. You can help by <a href="/wiki/Special:EditPage/Comparison_of_programming_languages_(associative_array)" title="Special:EditPage/Comparison of programming languages (associative array)">adding missing items</a> with <a href="/wiki/Wikipedia:Reliable_sources" title="Wikipedia:Reliable sources">reliable sources</a>.</div> The following is a comparison of <a href="/wiki/Associative_array" title="Associative array">associative arrays</a> (also "mapping", "hash", and "dictionary") in various programming languages. <div class="mw-heading mw-heading3"><h3 id="AWK">AWK</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=2" title="Edit section: AWK">edit</a>]</div> <a href="/wiki/AWK" title="AWK">AWK</a> has built-in, language-level support for associative arrays. For example: <div class="mw-highlight mw-highlight-lang-awk mw-content-ltr" dir="ltr"><pre>phonebook["Sally Smart"] = "555-9999" phonebook["John Doe"] = "555-1212" phonebook["J. Random Hacker"] = "555-1337" </pre></div> The following code loops through an associated array and prints its contents: <div class="mw-highlight mw-highlight-lang-awk mw-content-ltr" dir="ltr"><pre>for (name in phonebook) { print name, " ", phonebook[name] } </pre></div> The user can search for elements in an associative array, and delete elements from the array. The following shows how multi-dimensional associative arrays can be simulated in standard AWK using concatenation and the built-in string-separator variable SUBSEP: <div class="mw-highlight mw-highlight-lang-awk mw-content-ltr" dir="ltr"><pre>{ # for every input line multi[$1 SUBSEP $2]++; } # END { for (x in multi) { split(x, arr, SUBSEP); print arr[1], arr[2], multi[x]; } } </pre></div> <div class="mw-heading mw-heading3"><h3 id="C">C</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=3" title="Edit section: C">edit</a>]</div> There is no standard implementation of associative arrays in <a href="/wiki/C_(programming_language)" title="C (programming language)">C</a>, but a 3rd-party library, C Hash Table, with BSD license, is available.<a href="#cite_note-1">[1]</a> Another 3rd-party library, uthash, also creates associative arrays from C structures. A structure represents a value, and one of the structure fields serves as the key.<a href="#cite_note-2">[2]</a> Finally, the <a href="/wiki/GLib" title="GLib">GLib</a> library also supports associative arrays, along with many other advanced data types and is the recommended implementation of the GNU Project.<a href="#cite_note-3">[3]</a> Similar to <a href="/wiki/GLib" title="GLib">GLib</a>, <a href="/wiki/Apple_Inc." title="Apple Inc.">Apple</a>'s cross-platform <a href="/wiki/Core_Foundation" title="Core Foundation">Core Foundation</a> framework provides several basic data types. In particular, there are reference-counted CFDictionary and CFMutableDictionary. <div class="mw-heading mw-heading3"><h3 id="C#">C#</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=4" title="Edit section: C#">edit</a>]</div> <a href="/wiki/C_Sharp_(programming_language)" title="C Sharp (programming language)">C#</a> uses the collection classes provided by the <a href="/wiki/.NET_Framework" title=".NET Framework">.NET Framework</a>. The most commonly used associative array type is <code>System.Collections.Generic.Dictionary<TKey, TValue></code>, which is implemented as a mutable hash table. The relatively new <code>System.Collections.Immutable</code> package, available in .NET Framework versions 4.5 and above, and in all versions of <a href="/wiki/.NET_Core" class="mw-redirect" title=".NET Core">.NET Core</a>, also includes the <code>System.Collections.Immutable.Dictionary<TKey, TValue></code> type, which is implemented using an <a href="/wiki/AVL_tree" title="AVL tree">AVL tree</a>. The methods that would normally mutate the object in-place instead return a new object that represents the state of the original object after mutation. <div class="mw-heading mw-heading4"><h4 id="Creation">Creation</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=5" title="Edit section: Creation">edit</a>]</div> The following demonstrates three means of populating a mutable dictionary: <ul><li>the <code>Add</code> method, which adds a key and value and throws an <a href="/wiki/Exception_handling" title="Exception handling">exception</a> if the key already exists in the dictionary;</li> <li>assigning to the indexer, which overwrites any existing value, if present; and</li> <li>assigning to the backing property of the indexer, for which the indexer is <a href="/wiki/Syntactic_sugar" title="Syntactic sugar">syntactic sugar</a> (not applicable to C#, see <a href="#F#">F#</a> or <a href="#Visual_Basic_.NET">VB.NET</a> examples).</li></ul> <div class="mw-highlight mw-highlight-lang-csharp mw-content-ltr" dir="ltr"><pre>var dictionary = new Dictionary<string, string>(); dictionary.Add("Sally Smart", "555-9999"); dictionary["John Doe"] = "555-1212"; // Not allowed in C#. // dictionary.Item("J. Random Hacker") = "553-1337"; dictionary["J. Random Hacker"] = "553-1337"; </pre></div> The dictionary can also be initialized during construction using a "collection initializer", which compiles to repeated calls to <code>Add</code>. <div class="mw-highlight mw-highlight-lang-csharp mw-content-ltr" dir="ltr"><pre>var dictionary = new Dictionary<string, string> { { "Sally Smart", "555-9999" }, { "John Doe", "555-1212" }, { "J. Random Hacker", "553-1337" } }; </pre></div> <div class="mw-heading mw-heading4"><h4 id="Access_by_key">Access by key</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=6" title="Edit section: Access by key">edit</a>]</div> Values are primarily retrieved using the indexer (which throws an exception if the key does not exist) and the <code>TryGetValue</code> method, which has an output parameter for the sought value and a Boolean return-value indicating whether the key was found. <div class="mw-highlight mw-highlight-lang-csharp mw-content-ltr" dir="ltr"><pre>var sallyNumber = dictionary["Sally Smart"]; </pre></div> <div class="mw-highlight mw-highlight-lang-csharp mw-content-ltr" dir="ltr"><pre>var sallyNumber = (dictionary.TryGetValue("Sally Smart", out var result) ? result : "n/a"; </pre></div> In this example, the <code>sallyNumber</code> value will now contain the string <code>"555-9999"</code>. <div class="mw-heading mw-heading4"><h4 id="Enumeration">Enumeration</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=7" title="Edit section: Enumeration">edit</a>]</div> A dictionary can be viewed as a sequence of keys, sequence of values, or sequence of pairs of keys and values represented by instances of the <code>KeyValuePair<TKey, TValue></code> type, although there is no guarantee of order. For a sorted dictionary, the programmer could choose to use a <code>SortedDictionary<TKey, TValue></code> or use the <code>.Sort</code> <a href="/wiki/Language_Integrated_Query" title="Language Integrated Query">LINQ</a> extension method when enumerating. The following demonstrates enumeration using a <a href="/wiki/Foreach_loop" title="Foreach loop">foreach loop</a>: <div class="mw-highlight mw-highlight-lang-csharp mw-content-ltr" dir="ltr"><pre>// loop through the collection and display each entry. foreach (KeyValuePair<string,string> kvp in dictionary) { Console.WriteLine("Phone number for {0} is {1}", kvp.Key, kvp.Value); } </pre></div> <div class="mw-heading mw-heading3"><h3 id="C++">C++</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=8" title="Edit section: C++">edit</a>]</div> <a href="/wiki/C%2B%2B" title="C++">C++</a> has a form of associative array called <a href="/wiki/Map_(C%2B%2B)" class="mw-redirect" title="Map (C++)"><code>std::map</code></a> (see <a href="/wiki/Standard_Template_Library#Containers" title="Standard Template Library">Standard Template Library#Containers</a>). One could create a phone-book map with the following code in C++: <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>#include <map> #include <string> #include <utility> int main() { std::map<std::string, std::string> phone_book; phone_book.insert(std::make_pair("Sally Smart", "555-9999")); phone_book.insert(std::make_pair("John Doe", "555-1212")); phone_book.insert(std::make_pair("J. Random Hacker", "553-1337")); } </pre></div> Or less efficiently, as this creates temporary <code>std::string</code> values: <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>#include <map> #include <string> int main() { std::map<std::string, std::string> phone_book; phone_book["Sally Smart"] = "555-9999"; phone_book["John Doe"] = "555-1212"; phone_book["J. Random Hacker"] = "553-1337"; } </pre></div> With the extension of <a href="/wiki/C%2B%2B11#Initializer_lists" title="C++11">initialization lists</a> in C++11, entries can be added during a map's construction as shown below: <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>#include <map> #include <string> int main() { std::map<std::string, std::string> phone_book { {"Sally Smart", "555-9999"}, {"John Doe", "555-1212"}, {"J. Random Hacker", "553-1337"} }; } </pre></div> You can iterate through the list with the following code (C++03): <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>std::map<std::string, std::string>::iterator curr, end; for(curr = phone_book.begin(), end = phone_book.end(); curr != end; ++curr) std::cout << curr->first << " = " << curr->second << std::endl; </pre></div> The same task in C++11: <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>for(const auto& curr : phone_book) std::cout << curr.first << " = " << curr.second << std::endl; </pre></div> Using the structured binding available in <a href="/wiki/C%2B%2B17" title="C++17">C++17</a>: <div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>for (const auto& [name, number] : phone_book) { std::cout << name << " = " << number << std::endl; } </pre></div> In C++, the <code>std::map</code> class is <a href="/wiki/Generic_programming#Templates_in_C.2B.2B" title="Generic programming">templated</a> which allows the <a href="/wiki/Data_type" title="Data type">data types</a> of keys and values to be different for different <code>map</code> instances. For a given instance of the <code>map</code> class the keys must be of the same base type. The same must be true for all of the values. Although <code>std::map</code> is typically implemented using a <a href="/wiki/Self-balancing_binary_search_tree" title="Self-balancing binary search tree">self-balancing binary search tree</a>, C++11 defines a second map called <code><a href="/wiki/Std::unordered_map" class="mw-redirect" title="Std::unordered map">std::unordered_map</a></code>, which has the algorithmic characteristics of a hash table. This is a common vendor extension to the <a href="/wiki/Standard_Template_Library" title="Standard Template Library">Standard Template Library</a> (STL) as well, usually called <code>hash_map</code>, available from such implementations as SGI and STLPort. <div class="mw-heading mw-heading3"><h3 id="Cobra">Cobra</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=9" title="Edit section: Cobra">edit</a>]</div> Initializing an empty dictionary and adding items in <a href="/wiki/Cobra_(programming_language)" title="Cobra (programming language)">Cobra</a>: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>dic as Dictionary<of String, String> = Dictionary<of String, String>() dic.add('Sally Smart', '555-9999') dic.add('John Doe', '555-1212') dic.add('J. Random Hacker', '553-1337') assert dic['Sally Smart'] == '555-9999' </pre></div> Alternatively, a dictionary can be initialized with all items during construction: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>dic = { 'Sally Smart':'555-9999', 'John Doe':'555-1212', 'J. Random Hacker':'553-1337' } </pre></div> The dictionary can be enumerated by a for-loop, but there is no guaranteed order: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>for key, val in dic print "[key]'s phone number is [val]" </pre></div> <div class="mw-heading mw-heading3"><h3 id="ColdFusion_Markup_Language">ColdFusion Markup Language</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=10" title="Edit section: ColdFusion Markup Language">edit</a>]</div> A structure in <a href="/wiki/ColdFusion_Markup_Language" title="ColdFusion Markup Language">ColdFusion Markup Language</a> (CFML) is equivalent to an associative array: <div class="mw-highlight mw-highlight-lang-cfs mw-content-ltr" dir="ltr"><pre>dynamicKeyName = "John Doe"; phoneBook = { "Sally Smart" = "555-9999", "#dynamicKeyName#" = "555-4321", "J. Random Hacker" = "555-1337", UnknownComic = "???" }; writeOutput(phoneBook.UnknownComic); // ??? writeDump(phoneBook); // entire struct </pre></div> <div class="mw-heading mw-heading3"><h3 id="D">D</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=11" title="Edit section: D">edit</a>]</div> <a href="/wiki/D_programming_language" class="mw-redirect" title="D programming language">D</a> offers direct support for associative arrays in the core language; such arrays are implemented as a chaining hash table with binary trees.<a href="#cite_note-4">[4]</a> The equivalent example would be: <div class="mw-highlight mw-highlight-lang-d mw-content-ltr" dir="ltr"><pre>int main() { string[ string ] phone_book; phone_book["Sally Smart"] = "555-9999"; phone_book["John Doe"] = "555-1212"; phone_book["J. Random Hacker"] = "553-1337"; return 0; } </pre></div> Keys and values can be any types, but all the keys in an associative array must be of the same type, and the same goes for dependent values. Looping through all properties and associated values, and printing them, can be coded as follows: <div class="mw-highlight mw-highlight-lang-d mw-content-ltr" dir="ltr"><pre>foreach (key, value; phone_book) { writeln("Number for " ~ key ~ ": " ~ value ); } </pre></div> A property can be removed as follows: <div class="mw-highlight mw-highlight-lang-d mw-content-ltr" dir="ltr"><pre>phone_book.remove("Sally Smart"); </pre></div> <div class="mw-heading mw-heading3"><h3 id="Delphi">Delphi</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=12" title="Edit section: Delphi">edit</a>]</div> <a href="/wiki/Delphi_(software)" title="Delphi (software)">Delphi</a> supports several standard containers, including TDictionary<T>: <div class="mw-highlight mw-highlight-lang-delphi mw-content-ltr" dir="ltr"><pre>uses SysUtils, Generics.Collections; var PhoneBook: TDictionary<string, string>; Entry: TPair<string, string>; begin PhoneBook := TDictionary<string, string>.Create; PhoneBook.Add('Sally Smart', '555-9999'); PhoneBook.Add('John Doe', '555-1212'); PhoneBook.Add('J. Random Hacker', '553-1337'); for Entry in PhoneBook do Writeln(Format('Number for %s: %s',[Entry.Key, Entry.Value])); end. </pre></div> Pre-2009 Delphi versions do not support associative arrays directly. Such arrays can be simulated using the TStrings class: <div class="mw-highlight mw-highlight-lang-delphi mw-content-ltr" dir="ltr"><pre>procedure TForm1.Button1Click(Sender: TObject); var DataField: TStrings; i: Integer; begin DataField := TStringList.Create; DataField.Values['Sally Smart'] := '555-9999'; DataField.Values['John Doe'] := '555-1212'; DataField.Values['J. Random Hacker'] := '553-1337'; // access an entry and display it in a message box ShowMessage(DataField.Values['Sally Smart']); // loop through the associative array for i := 0 to DataField.Count - 1 do begin ShowMessage('Number for ' + DataField.Names[i] + ': ' + DataField.ValueFromIndex[i]); end; DataField.Free; end; </pre></div> <div class="mw-heading mw-heading3"><h3 id="Erlang">Erlang</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=13" title="Edit section: Erlang">edit</a>]</div> <a href="/wiki/Erlang_(programming_language)" title="Erlang (programming language)">Erlang</a> offers many ways to represent mappings; three of the most common in the standard library are keylists, dictionaries, and maps. <div class="mw-heading mw-heading4"><h4 id="Keylists">Keylists</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=14" title="Edit section: Keylists">edit</a>]</div> Keylists are lists of <a href="/wiki/Tuple" title="Tuple">tuples</a>, where the first element of each tuple is a key, and the second is a value. Functions for operating on keylists are provided in the <code>lists</code> module. <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>PhoneBook = [{"Sally Smith", "555-9999"}, {"John Doe", "555-1212"}, {"J. Random Hacker", "553-1337"}]. </pre></div> Accessing an element of the keylist can be done with the <code>lists:keyfind/3</code> function: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>{_, Phone} = lists:keyfind("Sally Smith", 1, PhoneBook), io:format("Phone number: ~s~n", [Phone]). </pre></div> <div class="mw-heading mw-heading4"><h4 id="Dictionaries">Dictionaries</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=15" title="Edit section: Dictionaries">edit</a>]</div> Dictionaries are implemented in the <code>dict</code> module of the standard library. A new dictionary is created using the <code>dict:new/0</code> function and new key/value pairs are stored using the <code>dict:store/3</code> function: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>PhoneBook1 = dict:new(), PhoneBook2 = dict:store("Sally Smith", "555-9999", Dict1), PhoneBook3 = dict:store("John Doe", "555-1212", Dict2), PhoneBook = dict:store("J. Random Hacker", "553-1337", Dict3). </pre></div> Such a serial initialization would be more idiomatically represented in Erlang with the appropriate function: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>PhoneBook = dict:from_list([{"Sally Smith", "555-9999"}, {"John Doe", "555-1212"}, {"J. Random Hacker", "553-1337"}]). </pre></div> The dictionary can be accessed using the <code>dict:find/2</code> function: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>{ok, Phone} = dict:find("Sally Smith", PhoneBook), io:format("Phone: ~s~n", [Phone]). </pre></div> In both cases, any Erlang term can be used as the key. Variations include the <code>orddict</code> module, implementing ordered dictionaries, and <code>gb_trees</code>, implementing general balanced trees. <div class="mw-heading mw-heading4"><h4 id="Maps">Maps</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=16" title="Edit section: Maps">edit</a>]</div> Maps were introduced in OTP 17.0,<a href="#cite_note-5">[5]</a> and combine the strengths of keylists and dictionaries. A map is defined using the syntax <code>#{ K1 => V1, ... Kn => Vn }</code>: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>PhoneBook = #{"Sally Smith" => "555-9999", "John Doe" => "555-1212", "J. Random Hacker" => "553-1337"}. </pre></div> Basic functions to interact with maps are available from the <code>maps</code> module. For example, the <code>maps:find/2</code> function returns the value associated with a key: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>{ok, Phone} = maps:find("Sally Smith", PhoneBook), io:format("Phone: ~s~n", [Phone]). </pre></div> Unlike dictionaries, maps can be pattern matched upon: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>#{"Sally Smith", Phone} = PhoneBook, io:format("Phone: ~s~n", [Phone]). </pre></div> Erlang also provides syntax sugar for functional updates—creating a new map based on an existing one, but with modified values or additional keys: <div class="mw-highlight mw-highlight-lang-erlang mw-content-ltr" dir="ltr"><pre>PhoneBook2 = PhoneBook#{ % the `:=` operator updates the value associated with an existing key "J. Random Hacker" := "355-7331", % the `=>` operator adds a new key-value pair, potentially replacing an existing one "Alice Wonderland" => "555-1865" } </pre></div> <div class="mw-heading mw-heading3"><h3 id="F#">F#</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=17" title="Edit section: F#">edit</a>]</div> <div class="mw-heading mw-heading4"><h4 id="Map<'Key,'Value>">Map<'Key,'Value></h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=18" title="Edit section: Map<'Key,'Value>">edit</a>]</div> At runtime, <a href="/wiki/F_Sharp_(programming_language)" title="F Sharp (programming language)">F#</a> provides the <code>Collections.Map<'Key,'Value></code> type, which is an immutable <a href="/wiki/AVL_tree" title="AVL tree">AVL tree</a>. <div class="mw-heading mw-heading5"><h5 id="Creation_2">Creation</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=19" title="Edit section: Creation">edit</a>]</div> The following example calls the <code>Map</code> constructor, which operates on a list (a semicolon delimited sequence of elements enclosed in square brackets) of tuples (which in F# are comma-delimited sequences of elements). <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let numbers = [ "Sally Smart", "555-9999"; "John Doe", "555-1212"; "J. Random Hacker", "555-1337" ] |> Map </pre></div> <div class="mw-heading mw-heading5"><h5 id="Access_by_key_2">Access by key</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=20" title="Edit section: Access by key">edit</a>]</div> Values can be looked up via one of the <code>Map</code> members, such as its indexer or <code>Item</code> property (which throw an <a href="/wiki/Exception_handling" title="Exception handling">exception</a> if the key does not exist) or the <code>TryFind</code> function, which returns an <a href="/wiki/Option_type" title="Option type">option type</a> with a value of <code>Some <result></code>, for a successful lookup, or <code>None</code>, for an unsuccessful one. <a href="/wiki/Pattern_matching" title="Pattern matching">Pattern matching</a> can then be used to extract the raw value from the result, or a default value can be set. <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let sallyNumber = numbers.["Sally Smart"] // or let sallyNumber = numbers.Item("Sally Smart") </pre></div> <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let sallyNumber = match numbers.TryFind("Sally Smart") with | Some(number) -> number | None -> "n/a" </pre></div> In both examples above, the <code>sallyNumber</code> value would contain the string <code>"555-9999"</code>. <div class="mw-heading mw-heading4"><h4 id="Dictionary<'TKey,'TValue>">Dictionary<'TKey,'TValue></h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=21" title="Edit section: Dictionary<'TKey,'TValue>">edit</a>]</div> Because F# is a .NET language, it also has access to features of the <a href="/wiki/.NET_Framework" title=".NET Framework">.NET Framework</a>, including the <code class="mw-highlight mw-highlight-lang-f# mw-content-ltr" style="" dir="ltr">System.Collections.Generic.Dictionary<'TKey,'TValue></code> type (which is implemented as a <a href="/wiki/Hash_table" title="Hash table">hash table</a>), which is the primary associative array type used in C# and Visual Basic. This type may be preferred when writing code that is intended to operate with other languages on the .NET Framework, or when the performance characteristics of a hash table are preferred over those of an AVL tree. <div class="mw-heading mw-heading5"><h5 id="Creation_3">Creation</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=22" title="Edit section: Creation">edit</a>]</div> The <code>dict</code> function provides a means of conveniently creating a .NET dictionary that is not intended to be mutated; it accepts a sequence of tuples and returns an immutable object that implements <code>IDictionary<'TKey,'TValue></code>. <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let numbers = [ "Sally Smart", "555-9999"; "John Doe", "555-1212"; "J. Random Hacker", "555-1337" ] |> dict </pre></div> When a mutable dictionary is needed, the constructor of <code class="mw-highlight mw-highlight-lang-f# mw-content-ltr" style="" dir="ltr">System.Collections.Generic.Dictionary<'TKey,'TValue></code> can be called directly. See <a href="#C#">the C# example on this page</a> for additional information. <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let numbers = System.Collections.Generic.Dictionary<string, string>() numbers.Add("Sally Smart", "555-9999") numbers.["John Doe"] <- "555-1212" numbers.Item("J. Random Hacker") <- "555-1337" </pre></div> <div class="mw-heading mw-heading5"><h5 id="Access_by_key_3">Access by key</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=23" title="Edit section: Access by key">edit</a>]</div> <code>IDictionary</code> instances have an indexer that is used in the same way as <code>Map</code>, although the equivalent to <code>TryFind</code> is <code>TryGetValue</code>, which has an output parameter for the sought value and a Boolean return value indicating whether the key was found. <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let sallyNumber = let mutable result = "" if numbers.TryGetValue("Sally Smart", &result) then result else "n/a" </pre></div> F# also allows the function to be called as if it had no output parameter and instead returned a tuple containing its regular return value and the value assigned to the output parameter: <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>let sallyNumber = match numbers.TryGetValue("Sally Smart") with | true, number -> number | _ -> "n/a" </pre></div> <div class="mw-heading mw-heading4"><h4 id="Enumeration_2">Enumeration</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=24" title="Edit section: Enumeration">edit</a>]</div> A dictionary or map can be enumerated using <code>Seq.map</code>. <div class="mw-highlight mw-highlight-lang-fsharp mw-content-ltr" dir="ltr"><pre>// loop through the collection and display each entry. numbers |> Seq.map (fun kvp -> printfn "Phone number for %O is %O" kvp.Key kvp.Value) </pre></div> <div class="mw-heading mw-heading3"><h3 id="FoxPro">FoxPro</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=25" title="Edit section: FoxPro">edit</a>]</div> <a href="/wiki/Visual_FoxPro" title="Visual FoxPro">Visual FoxPro</a> implements mapping with the Collection Class. <div class="mw-highlight mw-highlight-lang-foxpro mw-content-ltr" dir="ltr"><pre>mapping = NEWOBJECT("Collection") mapping.Add("Daffodils", "flower2") && Add(object, key) – key must be character index = mapping.GetKey("flower2") && returns the index value 1 object = mapping("flower2") && returns "Daffodils" (retrieve by key) object = mapping(1) && returns "Daffodils" (retrieve by index) </pre></div> GetKey returns 0 if the key is not found. <div class="mw-heading mw-heading3"><h3 id="Go">Go</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=26" title="Edit section: Go">edit</a>]</div> <a href="/wiki/Go_(programming_language)" title="Go (programming language)">Go</a> has built-in, language-level support for associative arrays, called "maps". A map's key type may only be a boolean, numeric, string, array, struct, pointer, interface, or channel type. A map type is written: <code>map[keytype]valuetype</code> Adding elements one at a time: <div class="mw-highlight mw-highlight-lang-go mw-content-ltr" dir="ltr"><pre>phone_book := make(map[string] string) // make an empty map phone_book["Sally Smart"] = "555-9999" phone_book["John Doe"] = "555-1212" phone_book["J. Random Hacker"] = "553-1337" </pre></div> A map literal: <div class="mw-highlight mw-highlight-lang-go mw-content-ltr" dir="ltr"><pre>phone_book := map[string] string { "Sally Smart": "555-9999", "John Doe": "555-1212", "J. Random Hacker": "553-1337", } </pre></div> Iterating through a map: <div class="mw-highlight mw-highlight-lang-go mw-content-ltr" dir="ltr"><pre>// over both keys and values for key, value := range phone_book { fmt.Printf("Number for %s: %s\n", key, value) } // over just keys for key := range phone_book { fmt.Printf("Name: %s\n", key) } </pre></div> <div class="mw-heading mw-heading3"><h3 id="Haskell">Haskell</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=27" title="Edit section: Haskell">edit</a>]</div> The <a href="/wiki/Haskell" title="Haskell">Haskell</a> programming language provides only one kind of associative container – a list of pairs: <div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>m = [("Sally Smart", "555-9999"), ("John Doe", "555-1212"), ("J. Random Hacker", "553-1337")] main = print (lookup "John Doe" m) </pre></div> output: <pre>Just "555-1212" </pre> Note that the lookup function returns a "Maybe" value, which is "Nothing" if not found, or "Just 'result'" when found. The <a href="/wiki/Glasgow_Haskell_Compiler" title="Glasgow Haskell Compiler">Glasgow Haskell Compiler</a> (GHC), the most commonly used implementation of Haskell, provides two more types of associative containers. Other implementations may also provide these. One is polymorphic functional maps (represented as immutable balanced binary trees): <div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>import qualified Data.Map as M m = M.insert "Sally Smart" "555-9999" M.empty m' = M.insert "John Doe" "555-1212" m m'' = M.insert "J. Random Hacker" "553-1337" m' main = print (M.lookup "John Doe" m'' :: Maybe String) </pre></div> output: <pre>Just "555-1212" </pre> A specialized version for integer keys also exists as Data.IntMap. Finally, a polymorphic hash table: <div class="mw-highlight mw-highlight-lang-haskell mw-content-ltr" dir="ltr"><pre>import qualified Data.HashTable as H main = do m <- H.new (==) H.hashString H.insert m "Sally Smart" "555-9999" H.insert m "John Doe" "555-1212" H.insert m "J. Random Hacker" "553-1337" foo <- H.lookup m "John Doe" print foo </pre></div> output: <pre>Just "555-1212" </pre> Lists of pairs and functional maps both provide a purely functional interface, which is more idiomatic in Haskell. In contrast, hash tables provide an imperative interface in the <a href="/wiki/Monad_(functional_programming)#IO_monad" title="Monad (functional programming)">IO monad</a>. <div class="mw-heading mw-heading3"><h3 id="Java">Java</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=28" title="Edit section: Java">edit</a>]</div> In <a href="/wiki/Java_(programming_language)" title="Java (programming language)">Java</a> associative arrays are implemented as "maps", which are part of the <a href="/wiki/Java_collections_framework" title="Java collections framework">Java collections framework</a>. Since <a href="/wiki/Java_Platform,_Standard_Edition" title="Java Platform, Standard Edition">J2SE</a> 5.0 and the introduction of <a href="/wiki/Generic_programming" title="Generic programming">generics</a> into Java, collections can have a type specified; for example, an associative array that maps strings to strings might be specified as follows: <div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>Map<String, String> phoneBook = new HashMap<String, String>(); phoneBook.put("Sally Smart", "555-9999"); phoneBook.put("John Doe", "555-1212"); phoneBook.put("J. Random Hacker", "555-1337"); </pre></div> The <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/Map.html#get(java.lang.Object)">get</a></code> method is used to access a key; for example, the value of the expression <code>phoneBook.get("Sally Smart")</code> is <code>"555-9999"</code>. This code uses a hash map to store the associative array, by calling the constructor of the <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/HashMap.html">HashMap</a></code> class. However, since the code only uses methods common to the interface <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/Map.html">Map</a></code>, a self-balancing binary tree could be used by calling the constructor of the <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/TreeMap.html">TreeMap</a></code> class (which implements the subinterface <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/SortedMap.html">SortedMap</a></code>), without changing the definition of the <code>phoneBook</code> variable, or the rest of the code, or using other underlying data structures that implement the <code>Map</code> interface. The hash function in Java, used by HashMap and HashSet, is provided by the <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Object.html#hashCode()">Object.hashCode()</a></code> method. Since every class in Java <a href="/wiki/Inheritance_(object-oriented_programming)" title="Inheritance (object-oriented programming)">inherits</a> from <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Object.html">Object</a></code>, every object has a hash function. A class can <a href="/wiki/Method_overriding_(programming)" class="mw-redirect" title="Method overriding (programming)">override</a> the default implementation of <code>hashCode()</code> to provide a custom hash function more in accordance with the properties of the object. The <code>Object</code> class also contains the <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)">equals(Object)</a></code> method, which tests an object for equality with another object. Hashed data structures in Java rely on objects maintaining the following contract between their <code>hashCode()</code> and <code>equals()</code> methods: For two objects a and b, <div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>a.equals(b) == b.equals(a) if a.equals(b), then a.hashCode() == b.hashCode() </pre></div> In order to maintain this contract, a class that overrides <code>equals()</code> must also override <code>hashCode()</code>, and vice versa, so that <code>hashCode()</code> is based on the same properties (or a subset of the properties) as <code>equals()</code>. A further contract that a hashed data structure has with the object is that the results of the <code>hashCode()</code> and <code>equals()</code> methods will not change once the object has been inserted into the map. For this reason, it is generally a good practice to base the hash function on <a href="/wiki/Immutable_object" title="Immutable object">immutable</a> properties of the object. Analogously, TreeMap, and other sorted data structures, require that an ordering be defined on the data type. Either the data type must already have defined its own ordering, by implementing the <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/lang/Comparable.html">Comparable</a></code> interface; or a custom <code><a rel="nofollow" class="external text" href="https://docs.oracle.com/en/java/javase/19/docs/api/java.base/java/util/Comparator.html">Comparator</a></code> must be provided at the time the map is constructed. As with HashMap above, the relative ordering of keys in a TreeMap should not change once they have been inserted into the map. <div class="mw-heading mw-heading3"><h3 id="JavaScript">JavaScript</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=29" title="Edit section: JavaScript">edit</a>]</div> <a href="/wiki/JavaScript" title="JavaScript">JavaScript</a> (and its standardized version, <a href="/wiki/ECMAScript" title="ECMAScript">ECMAScript</a>) is a <a href="/wiki/Prototype-based_programming" title="Prototype-based programming">prototype-based</a> <a href="/wiki/Object-oriented_programming" title="Object-oriented programming">object-oriented</a> language. <div class="mw-heading mw-heading4"><h4 id="Map_and_WeakMap">Map and WeakMap</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=30" title="Edit section: Map and WeakMap">edit</a>]</div> Modern JavaScript handles associative arrays, using the <code>Map</code> and <code>WeakMap</code> classes. A map does not contain any keys by default; it only contains what is explicitly put into it. The keys and values can be any type (including functions, objects, or any primitive). <div class="mw-heading mw-heading5"><h5 id="Creation_4">Creation</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=31" title="Edit section: Creation">edit</a>]</div> A map can be initialized with all items during construction: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>const phoneBook = new Map([ ["Sally Smart", "555-9999"], ["John Doe", "555-1212"], ["J. Random Hacker", "553-1337"], ]); </pre></div> Alternatively, you can initialize an empty map and then add items: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>const phoneBook = new Map(); phoneBook.set("Sally Smart", "555-9999"); phoneBook.set("John Doe", "555-1212"); phoneBook.set("J. Random Hacker", "553-1337"); </pre></div> <div class="mw-heading mw-heading5"><h5 id="Access_by_key_4">Access by key</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=32" title="Edit section: Access by key">edit</a>]</div> Accessing an element of the map can be done with the <code>get</code> method: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>const sallyNumber = phoneBook.get("Sally Smart"); </pre></div> In this example, the value <code>sallyNumber</code> will now contain the string "555-9999". <div class="mw-heading mw-heading5"><h5 id="Enumeration_3">Enumeration</h5>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=33" title="Edit section: Enumeration">edit</a>]</div> The keys in a map are ordered. Thus, when iterating through it, a map object returns keys in order of insertion. The following demonstrates enumeration using a for-loop: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>// loop through the collection and display each entry. for (const [name, number] of phoneBook) { console.log(`Phone number for ${name} is ${number}`); } </pre></div> A key can be removed as follows: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>phoneBook.delete("Sally Smart"); </pre></div> <div class="mw-heading mw-heading4"><h4 id="Object">Object</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=34" title="Edit section: Object">edit</a>]</div> An object is similar to a map—both let you set keys to values, retrieve those values, delete keys, and detect whether a value is stored at a key. For this reason (and because there were no built-in alternatives), objects historically have been used as maps. However, there are important differences that make a map preferable in certain cases. In JavaScript an object is a mapping from property names to values—that is, an associative array with one caveat: the keys of an object must be either a string or a symbol (native objects and primitives implicitly converted to a string keys are allowed). Objects also include one feature unrelated to associative arrays: an object has a prototype, so it contains default keys that could conflict with user-defined keys. So, doing a lookup for a property will point the lookup to the prototype's definition if the object does not define the property. An object literal is written as <code>{ property1: value1, property2: value2, ... }</code>. For example: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>const myObject = { "Sally Smart": "555-9999", "John Doe": "555-1212", "J. Random Hacker": "553-1337", }; </pre></div> To prevent the lookup from using the prototype's properties, you can use the <code>Object.setPrototypeOf</code> function: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>Object.setPrototypeOf(myObject, null); </pre></div> As of ECMAScript 5 (ES5), the prototype can also be bypassed by using <code>Object.create(null)</code>: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>const myObject = Object.create(null); Object.assign(myObject, { "Sally Smart": "555-9999", "John Doe": "555-1212", "J. Random Hacker": "553-1337", }); </pre></div> If the property name is a valid identifier, the quotes can be omitted, e.g.: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>const myOtherObject = { foo: 42, bar: false }; </pre></div> Lookup is written using property-access notation, either square brackets, which always work, or dot notation, which only works for identifier keys: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>myObject["John Doe"] myOtherObject.foo </pre></div> You can also loop through all enumerable properties and associated values as follows (a for-in loop): <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>for (const property in myObject) { const value = myObject[property]; console.log(`myObject[${property}] = ${value}`); } </pre></div> Or (a for-of loop): <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>for (const [property, value] of Object.entries(myObject)) { console.log(`${property} = ${value}`); } </pre></div> A property can be removed as follows: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>delete myObject["Sally Smart"]; </pre></div> As mentioned before, properties are strings and symbols. Since every native object and primitive can be implicitly converted to a string, you can do: <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>myObject[1] // key is "1"; note that myObject[1] == myObject["1"] myObject[["a", "b"]] // key is "a,b" myObject[{ toString() { return "hello world"; } }] // key is "hello world" </pre></div> In modern JavaScript it's considered bad form to use the Array type as an associative array. Consensus is that the Object type and <code>Map</code>/<code>WeakMap</code> classes are best for this purpose. The reasoning behind this is that if Array is extended via prototype and Object is kept pristine, for and for-in loops will work as expected on associative 'arrays'. This issue has been brought to the fore by the popularity of JavaScript frameworks that make heavy and sometimes indiscriminate use of prototypes to extend JavaScript's inbuilt types. See <a rel="nofollow" class="external text" href="http://blog.metawrap.com/2006/05/30/june-6th-is-javascript-array-and-object-prototype-awareness-day/">JavaScript Array And Object Prototype Awareness Day</a> for more information on the issue. <div class="mw-heading mw-heading3"><h3 id="Julia">Julia</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=35" title="Edit section: Julia">edit</a>]</div> In <a href="/wiki/Julia_(programming_language)" title="Julia (programming language)">Julia</a>, the following operations manage associative arrays. Declare dictionary: <div class="mw-highlight mw-highlight-lang-julia mw-content-ltr" dir="ltr"><pre>phonebook = Dict( "Sally Smart" => "555-9999", "John Doe" => "555-1212", "J. Random Hacker" => "555-1337" ) </pre></div> Access element: <div class="mw-highlight mw-highlight-lang-julia mw-content-ltr" dir="ltr"><pre>phonebook["Sally Smart"] </pre></div> Add element: <div class="mw-highlight mw-highlight-lang-julia mw-content-ltr" dir="ltr"><pre>phonebook["New Contact"] = "555-2222" </pre></div> Delete element: <div class="mw-highlight mw-highlight-lang-julia mw-content-ltr" dir="ltr"><pre>delete!(phonebook, "Sally Smart") </pre></div> Get keys and values as <a href="/wiki/Iterator#Implicit_iterators" title="Iterator">iterables</a>: <div class="mw-highlight mw-highlight-lang-julia mw-content-ltr" dir="ltr"><pre>keys(phonebook) values(phonebook) </pre></div> <div class="mw-heading mw-heading3"><h3 id="KornShell_93,_and_compliant_shells">KornShell 93, and compliant shells</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=36" title="Edit section: KornShell 93, and compliant shells">edit</a>]</div> In <a href="/wiki/Korn_Shell" class="mw-redirect" title="Korn Shell">KornShell</a> 93, and compliant shells (ksh93, bash4...), the following operations can be used with associative arrays. Definition: <div class="mw-highlight mw-highlight-lang-ksh mw-content-ltr" dir="ltr"><pre>typeset -A phonebook; # ksh93; in bash4+, "typeset" is a synonym of the more preferred "declare", which works identically in this case phonebook=(["Sally Smart"]="555-9999" ["John Doe"]="555-1212" ["[[J. Random Hacker]]"]="555-1337"); </pre></div> Dereference: <div class="mw-highlight mw-highlight-lang-ksh mw-content-ltr" dir="ltr"><pre>${phonebook["John Doe"]}; </pre></div> <div class="mw-heading mw-heading3"><h3 id="Lisp">Lisp</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=37" title="Edit section: Lisp">edit</a>]</div> <a href="/wiki/Lisp_programming_language" class="mw-redirect" title="Lisp programming language">Lisp</a> was originally conceived as a "LISt Processing" language, and one of its most important data types is the linked list, which can be treated as an <a href="/wiki/Association_list" title="Association list">association list</a> ("alist"). <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>'(("Sally Smart" . "555-9999") ("John Doe" . "555-1212") ("J. Random Hacker" . "553-1337")) </pre></div> The syntax <code>(x . y)</code> is used to indicate a <a href="/wiki/Cons" title="Cons"><code>cons</code>ed</a> pair. Keys and values need not be the same type within an alist. Lisp and <a href="/wiki/Scheme_(programming_language)" title="Scheme (programming language)">Scheme</a> provide operators such as <code>assoc</code> to manipulate alists in ways similar to associative arrays. A set of operations specific to the handling of association lists exists for <a href="/wiki/Common_Lisp" title="Common Lisp">Common Lisp</a>, each of these working non-destructively. To add an entry the <code>acons</code> function is employed, creating and returning a new association list. An association list in Common Lisp mimicks a stack, that is, adheres to the last-in-first-out (LIFO) principle, and hence prepends to the list head. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(let ((phone-book NIL)) (setf phone-book (acons "Sally Smart" "555-9999" phone-book)) (setf phone-book (acons "John Doe" "555-1212" phone-book)) (setf phone-book (acons "J. Random Hacker" "555-1337" phone-book))) </pre></div> This function can be construed as an accommodation for <code>cons</code> operations.<a href="#cite_note-6">[6]</a> <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; The effect of ;; (cons (cons KEY VALUE) ALIST) ;; is equivalent to ;; (acons KEY VALUE ALIST) (let ((phone-book '(("Sally Smart" . "555-9999") ("John Doe" . "555-1212")))) (cons (cons "J. Random Hacker" "555-1337") phone-book)) </pre></div> Of course, the destructive <code>push</code> operation also allows inserting entries into an association list, an entry having to constitute a key-value cons in order to retain the mapping's validity. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(push (cons "Dummy" "123-4567") phone-book) </pre></div> Searching for an entry by its key is performed via <code>assoc</code>, which might be configured for the test predicate and direction, especially searching the association list from its end to its front. The result, if positive, returns the entire entry cons, not only its value. Failure to obtain a matching key leads to a return of the <code>NIL</code> value. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(assoc "John Doe" phone-book :test #'string=) </pre></div> Two generalizations of <code>assoc</code> exist: <code>assoc-if</code> expects a predicate function that tests each entry's key, returning the first entry for which the predicate produces a non-<code>NIL</code> value upon invocation. <code>assoc-if-not</code> inverts the logic, accepting the same arguments, but returning the first entry generating <code>NIL</code>. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Find the first entry whose key equals "John Doe". (assoc-if #'(lambda (key) (string= key "John Doe")) phone-book) ;; Finds the first entry whose key is neither "Sally Smart" nor "John Doe" (assoc-if-not #'(lambda (key) (member key '("Sally Smart" "John Doe") :test #'string=)) phone-book) </pre></div> The inverse process, the detection of an entry by its value, utilizes <code>rassoc</code>. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Find the first entry with a value of "555-9999". ;; We test the entry string values with the "string=" predicate. (rassoc "555-9999" phone-book :test #'string=) </pre></div> The corresponding generalizations <code>rassoc-if</code> and <code>rassoc-if-not</code> exist. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Finds the first entry whose value is "555-9999". (rassoc-if #'(lambda (value) (string= value "555-9999")) phone-book) ;; Finds the first entry whose value is not "555-9999". (rassoc-if-not #'(lambda (value) (string= value "555-9999")) phone-book) </pre></div> All of the previous entry search functions can be replaced by general list-centric variants, such as <code>find</code>, <code>find-if</code>, <code>find-if-not</code>, as well as pertinent functions like <code>position</code> and its derivates. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Find an entry with the key "John Doe" and the value "555-1212". (find (cons "John Doe" "555-1212") phone-book :test #'equal) </pre></div> Deletion, lacking a specific counterpart, is based upon the list facilities, including destructive ones. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Create and return an alist without any entry whose key equals "John Doe". (remove-if #'(lambda (entry) (string= (car entry) "John Doe")) phone-book) </pre></div> Iteration is accomplished with the aid of any function that expects a list. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Iterate via "map". (map NIL #'(lambda (entry) (destructuring-bind (key . value) entry (format T "~&~s => ~s" key value))) phone-book) ;; Iterate via "dolist". (dolist (entry phone-book) (destructuring-bind (key . value) entry (format T "~&~s => ~s" key value))) </pre></div> These being structured lists, processing and transformation operations can be applied without constraints. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Return a vector of the "phone-book" values. (map 'vector #'cdr phone-book) ;; Destructively modify the "phone-book" via "map-into". (map-into phone-book #'(lambda (entry) (destructuring-bind (key . value) entry (cons (reverse key) (reverse value)))) phone-book) </pre></div> Because of their linear nature, alists are used for relatively small sets of data. <a href="/wiki/Common_Lisp" title="Common Lisp">Common Lisp</a> also supports a <a href="/wiki/Hash_table" title="Hash table">hash table</a> data type, and for <a href="/wiki/Scheme_(programming_language)" title="Scheme (programming language)">Scheme</a> they are implemented in <a href="/wiki/Scheme_Requests_for_Implementation" title="Scheme Requests for Implementation">SRFI</a> 69. Hash tables have greater overhead than alists, but provide much faster access when there are many elements. A further characteristic is the fact that Common Lisp hash tables do not, as opposed to association lists, maintain the order of entry insertion. Common Lisp hash tables are constructed via the <code>make-hash-table</code> function, whose arguments encompass, among other configurations, a predicate to test the entry key. While tolerating arbitrary objects, even heterogeneity within a single hash table instance, the specification of this key <code>:test</code> function is confined to distinguishable entities: the Common Lisp standard only mandates the support of <code>eq</code>, <code>eql</code>, <code>equal</code>, and <code>equalp</code>, yet designating additional or custom operations as permissive for concrete implementations. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(let ((phone-book (make-hash-table :test #'equal))) (setf (gethash "Sally Smart" phone-book) "555-9999") (setf (gethash "John Doe" phone-book) "555-1212") (setf (gethash "J. Random Hacker" phone-book) "553-1337")) </pre></div> The <code>gethash</code> function permits obtaining the value associated with a key. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(gethash "John Doe" phone-book) </pre></div> Additionally, a default value for the case of an absent key may be specified. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(gethash "Incognito" phone-book 'no-such-key) </pre></div> An invocation of <code>gethash</code> actually returns two values: the value or substitute value for the key and a boolean indicator, returning <code>T</code> if the hash table contains the key and <code>NIL</code> to signal its absence. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(multiple-value-bind (value contains-key) (gethash "Sally Smart" phone-book) (if contains-key (format T "~&The associated value is: ~s" value) (format T "~&The key could not be found."))) </pre></div> Use <code>remhash</code> for deleting the entry associated with a key. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(remhash "J. Random Hacker" phone-book) </pre></div> <code>clrhash</code> completely empties the hash table. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(clrhash phone-book) </pre></div> The dedicated <code>maphash</code> function specializes in iterating hash tables. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(maphash #'(lambda (key value) (format T "~&~s => ~s" key value)) phone-book) </pre></div> Alternatively, the <code>loop</code> construct makes provisions for iterations, through keys, values, or conjunctions of both. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>;; Iterate the keys and values of the hash table. (loop for key being the hash-keys of phone-book using (hash-value value) do (format T "~&~s => ~s" key value)) ;; Iterate the values of the hash table. (loop for value being the hash-values of phone-book do (print value)) </pre></div> A further option invokes <code>with-hash-table-iterator</code>, an iterator-creating macro, the processing of which is intended to be driven by the caller. <div class="mw-highlight mw-highlight-lang-lisp mw-content-ltr" dir="ltr"><pre>(with-hash-table-iterator (entry-generator phone-book) (loop do (multiple-value-bind (has-entry key value) (entry-generator) (if has-entry (format T "~&~s => ~s" key value) (loop-finish))))) </pre></div> It is easy to construct composite abstract data types in Lisp, using structures or object-oriented programming features, in conjunction with lists, arrays, and hash tables. <div class="mw-heading mw-heading3"><h3 id="LPC">LPC</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=38" title="Edit section: LPC">edit</a>]</div> <a href="/wiki/LPC_(programming_language)" class="mw-redirect" title="LPC (programming language)">LPC</a> implements associative arrays as a fundamental type known as either "map" or "mapping", depending on the driver. The keys and values can be of any type. A mapping literal is written as <code>([ key_1 : value_1, key_2 : value_2 ])</code>. Procedural code looks like: <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>mapping phone_book = ([]); phone_book["Sally Smart"] = "555-9999"; phone_book["John Doe"] = "555-1212"; phone_book["J. Random Hacker"] = "555-1337"; </pre></div> Mappings are accessed for reading using the indexing operator in the same way as they are for writing, as shown above. So phone_book["Sally Smart"] would return the string "555-9999", and phone_book["John Smith"] would return 0. Testing for presence is done using the function member(), e.g. <code>if(member(phone_book, "John Smith")) write("John Smith is listed.\n");</code> Deletion is accomplished using a function called either m_delete() or map_delete(), depending on the driver: <code>m_delete(phone_book, "Sally Smart");</code> LPC drivers of the <a href="/wiki/LPMud#Amylaar" title="LPMud">Amylaar</a> family implement multivalued mappings using a secondary, numeric index (other drivers of the <a href="/wiki/MudOS" class="mw-redirect" title="MudOS">MudOS</a> family do not support multivalued mappings.) Example syntax: <div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>mapping phone_book = ([:2]); phone_book["Sally Smart", 0] = "555-9999"; phone_book["Sally Smart", 1] = "99 Sharp Way"; phone_book["John Doe", 0] = "555-1212"; phone_book["John Doe", 1] = "3 Nigma Drive"; phone_book["J. Random Hacker", 0] = "555-1337"; phone_book["J. Random Hacker", 1] = "77 Massachusetts Avenue"; </pre></div> LPC drivers modern enough to support a foreach() construct use it to iterate through their mapping types. <div class="mw-heading mw-heading3"><h3 id="Lua">Lua</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=39" title="Edit section: Lua">edit</a>]</div> In <a href="/wiki/Lua_programming_language" class="mw-redirect" title="Lua programming language">Lua</a>, "table" is a fundamental type that can be used either as an array (numerical index, fast) or as an associative array. The keys and values can be of any type, except nil. The following focuses on non-numerical indexes. A table literal is written as <code>{ value, key = value, [index] = value, ["non id string"] = value }</code>. For example: <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>phone_book = { ["Sally Smart"] = "555-9999", ["John Doe"] = "555-1212", ["J. Random Hacker"] = "553-1337", -- Trailing comma is OK } aTable = { -- Table as value subTable = { 5, 7.5, k = true }, -- key is "subTable" -- Function as value ['John Doe'] = function (age) if age < 18 then return "Young" else return "Old!" end end, -- Table and function (and other types) can also be used as keys } </pre></div> If the key is a valid identifier (not a reserved word), the quotes can be omitted. Identifiers are case sensitive. Lookup is written using either square brackets, which always works, or dot notation, which only works for identifier keys: <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>print(aTable["John Doe"](45)) x = aTable.subTable.k </pre></div> You can also loop through all keys and associated values with iterators or for-loops: <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>simple = { [true] = 1, [false] = 0, [3.14] = math.pi, x = 'x', ["!"] = 42 } function FormatElement(key, value) return "[" .. tostring(key) .. "] = " .. value .. ", " end -- Iterate on all keys table.foreach(simple, function (k, v) io.write(FormatElement(k, v)) end) print"" for k, v in pairs(simple) do io.write(FormatElement(k, v)) end print"" k= nil repeat k, v = next(simple, k) if k ~= nil then io.write(FormatElement(k, v)) end until k == nil print"" </pre></div> An entry can be removed by setting it to nil: <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>simple.x = nil </pre></div> Likewise, you can overwrite values or add them: <div class="mw-highlight mw-highlight-lang-lua mw-content-ltr" dir="ltr"><pre>simple['%'] = "percent" simple['!'] = 111 </pre></div> <div class="mw-heading mw-heading3"><h3 id="Mathematica_and_Wolfram_Language">Mathematica and Wolfram Language</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=40" title="Edit section: Mathematica and Wolfram Language">edit</a>]</div> <a href="/wiki/Mathematica" class="mw-redirect" title="Mathematica">Mathematica</a> and <a href="/wiki/Wolfram_Language" title="Wolfram Language">Wolfram Language</a> use the Association expression to represent associative arrays.<a href="#cite_note-7">[7]</a> <div class="mw-highlight mw-highlight-lang-mathematica mw-content-ltr" dir="ltr"><pre>phonebook = <| "Sally Smart" -> "555-9999", "John Doe" -> "555-1212", "J. Random Hacker" -> "553-1337" |>; </pre></div> To access:<a href="#cite_note-8">[8]</a> <div class="mw-highlight mw-highlight-lang-mathematica mw-content-ltr" dir="ltr"><pre>phonebook[[Key["Sally Smart"]]] </pre></div> If the keys are strings, the Key keyword is not necessary, so: <div class="mw-highlight mw-highlight-lang-mathematica mw-content-ltr" dir="ltr"><pre>phonebook[["Sally Smart"]] </pre></div> To list keys:<a href="#cite_note-9">[9]</a> and values<a href="#cite_note-10">[10]</a> <pre>Keys[phonebook] Values[phonebook] </pre> <div class="mw-heading mw-heading3"><h3 id="MUMPS">MUMPS</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=41" title="Edit section: MUMPS">edit</a>]</div> In <a href="/wiki/MUMPS" title="MUMPS">MUMPS</a> every array is an associative array. The built-in, language-level, direct support for associative arrays applies to private, process-specific arrays stored in memory called "locals" as well as to the permanent, shared, global arrays stored on disk which are available concurrently to multiple jobs. The name for globals is preceded by the circumflex "^" to distinguish them from local variables. <pre>SET ^phonebook("Sally Smart")="555-9999"  ;; storing permanent data SET phonebook("John Doe")="555-1212"  ;; storing temporary data SET phonebook("J. Random Hacker")="553-1337"  ;; storing temporary data MERGE ^phonebook=phonebook  ;; copying temporary data into permanent data </pre> Accessing the value of an element simply requires using the name with the subscript: <pre>WRITE "Phone Number :",^phonebook("Sally Smart"),! </pre> You can also loop through an associated array as follows: <pre>SET NAME="" FOR S NAME=$ORDER(^phonebook(NAME)) QUIT:NAME="" WRITE NAME," Phone Number :",^phonebook(NAME),! </pre> <div class="mw-heading mw-heading3"><h3 id="Objective-C_(Cocoa/GNUstep)">Objective-C (Cocoa/GNUstep)</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=42" title="Edit section: Objective-C (Cocoa/GNUstep)">edit</a>]</div> <a href="/wiki/Cocoa_(API)" title="Cocoa (API)">Cocoa</a> and <a href="/wiki/GNUstep" title="GNUstep">GNUstep</a>, written in <a href="/wiki/Objective-C" title="Objective-C">Objective-C</a>, handle associative arrays using <code>NSMutableDictionary</code> (a mutable version of <code>NSDictionary</code>) class cluster. This class allows assignments between any two objects. A copy of the key object is made before it is inserted into <code>NSMutableDictionary</code>, therefore the keys must conform to the <code>NSCopying</code> protocol. When being inserted to a dictionary, the value object receives a retain message to increase its reference count. The value object will receive the release message when it will be deleted from the dictionary (either explicitly or by adding to the dictionary a different object with the same key). <div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>NSMutableDictionary *aDictionary = [[NSMutableDictionary alloc] init]; [aDictionary setObject:@"555-9999" forKey:@"Sally Smart"]; [aDictionary setObject:@"555-1212" forKey:@"John Doe"]; [aDictionary setObject:@"553-1337" forKey:@"Random Hacker"]; </pre></div> To access assigned objects, this command may be used: <div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>id anObject = [aDictionary objectForKey:@"Sally Smart"]; </pre></div> All keys or values can be enumerated using <code>NSEnumerator</code>: <div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>NSEnumerator *keyEnumerator = [aDictionary keyEnumerator]; id key; while ((key = [keyEnumerator nextObject])) { // ... process it here ... } </pre></div> In Mac OS X 10.5+ and iPhone OS, dictionary keys can be enumerated more concisely using the <code>NSFastEnumeration</code> construct:<a href="#cite_note-11">[11]</a> <div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>for (id key in aDictionary) { // ... process it here ... } </pre></div> What is even more practical, structured data graphs may be easily created using <a href="/wiki/Cocoa_(API)" title="Cocoa (API)">Cocoa</a>, especially <code>NSDictionary</code> (<code>NSMutableDictionary</code>). This can be illustrated with this compact example: <div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>NSDictionary *aDictionary = [NSDictionary dictionaryWithObjectsAndKeys: [NSDictionary dictionaryWithObjectsAndKeys: @"555-9999", @"Sally Smart", @"555-1212", @"John Doe", nil], @"students", [NSDictionary dictionaryWithObjectsAndKeys: @"553-1337", @"Random Hacker", nil], @"hackers", nil]; </pre></div> Relevant fields can be quickly accessed using key paths: <div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>id anObject = [aDictionary valueForKeyPath:@"students.Sally Smart"]; </pre></div> <div class="mw-heading mw-heading3"><h3 id="OCaml">OCaml</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=43" title="Edit section: OCaml">edit</a>]</div> The <a href="/wiki/OCaml" title="OCaml">OCaml</a> programming language provides three different associative containers. The simplest is a list of pairs: <div class="mw-highlight mw-highlight-lang-ocaml mw-content-ltr" dir="ltr"><pre># let m = [ "Sally Smart", "555-9999"; "John Doe", "555-1212"; "J. Random Hacker", "553-1337"];; val m : (string * string) list = [ ("Sally Smart", "555-9999"); ("John Doe", "555-1212"); ("J. Random Hacker", "553-1337") ] # List.assoc "John Doe" m;; - : string = "555-1212" </pre></div> The second is a polymorphic hash table: <div class="mw-highlight mw-highlight-lang-ocaml mw-content-ltr" dir="ltr"><pre># let m = Hashtbl.create 3;; val m : ('_a, '_b) Hashtbl.t = <abstr> # Hashtbl.add m "Sally Smart" "555-9999"; Hashtbl.add m "John Doe" "555-1212"; Hashtbl.add m "J. Random Hacker" "553-1337";; - : unit = () # Hashtbl.find m "John Doe";; - : string = "555-1212" </pre></div> The code above uses OCaml's default hash function <code>Hashtbl.hash</code>, which is defined automatically for all types. To use a modified hash function, use the functor interface <code>Hashtbl.Make</code> to create a module, such as with <code>Map</code>. Finally, functional maps (represented as immutable balanced binary trees): <div class="mw-highlight mw-highlight-lang-ocaml mw-content-ltr" dir="ltr"><pre># module StringMap = Map.Make(String);; ... # let m = StringMap.add "Sally Smart" "555-9999" StringMap.empty let m = StringMap.add "John Doe" "555-1212" m let m = StringMap.add "J. Random Hacker" "553-1337" m;; val m : string StringMap.t = <abstr> # StringMap.find "John Doe" m;; - : string = "555-1212" </pre></div> Note that in order to use <code>Map</code>, you have to provide the functor <code>Map.Make</code> with a module which defines the key type and the comparison function. The third-party library ExtLib provides a polymorphic version of functional maps, called <code>PMap</code>,<a href="#cite_note-12">[12]</a> which is given a comparison function upon creation. Lists of pairs and functional maps both provide a purely functional interface. By contrast, hash tables provide an imperative interface. For many operations, hash tables are significantly faster than lists of pairs and functional maps. <div class="mw-heading mw-heading3"><h3 id="OptimJ">OptimJ</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=44" title="Edit section: OptimJ">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1251242444">.mw-parser-output .ambox{border:1px solid #a2a9b1;border-left:10px solid #36c;background-color:#fbfbfb;box-sizing:border-box}.mw-parser-output .ambox+link+.ambox,.mw-parser-output .ambox+link+style+.ambox,.mw-parser-output .ambox+link+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+style+.ambox,.mw-parser-output .ambox+.mw-empty-elt+link+link+.ambox{margin-top:-1px}html body.mediawiki .mw-parser-output .ambox.mbox-small-left{margin:4px 1em 4px 0;overflow:hidden;width:238px;border-collapse:collapse;font-size:88%;line-height:1.25em}.mw-parser-output .ambox-speedy{border-left:10px solid #b32424;background-color:#fee7e6}.mw-parser-output .ambox-delete{border-left:10px solid #b32424}.mw-parser-output .ambox-content{border-left:10px solid #f28500}.mw-parser-output .ambox-style{border-left:10px solid #fc3}.mw-parser-output .ambox-move{border-left:10px solid #9932cc}.mw-parser-output .ambox-protection{border-left:10px solid #a2a9b1}.mw-parser-output .ambox .mbox-text{border:none;padding:0.25em 0.5em;width:100%}.mw-parser-output .ambox .mbox-image{border:none;padding:2px 0 2px 0.5em;text-align:center}.mw-parser-output .ambox .mbox-imageright{border:none;padding:2px 0.5em 2px 0;text-align:center}.mw-parser-output .ambox .mbox-empty-cell{border:none;padding:0;width:1px}.mw-parser-output .ambox .mbox-image-div{width:52px}@media(min-width:720px){.mw-parser-output .ambox{margin:0 10%}}@media print{body.ns-0 .mw-parser-output .ambox{display:none!important}}</style><table class="box-More_citations_needed_section plainlinks metadata ambox ambox-content ambox-Refimprove" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><a href="/wiki/File:Question_book-new.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png" decoding="async" width="50" height="39" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/75px-Question_book-new.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/100px-Question_book-new.svg.png 2x" data-file-width="512" data-file-height="399" /></a></div></td><td class="mbox-text"><div class="mbox-text-span">This section needs additional citations for <a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability">verification</a>. Please help <a href="/wiki/Special:EditPage/Comparison_of_programming_languages_(associative_array)" title="Special:EditPage/Comparison of programming languages (associative array)">improve this article</a> by <a href="/wiki/Help:Referencing_for_beginners" title="Help:Referencing for beginners">adding citations to reliable sources</a> in this section. Unsourced material may be challenged and removed. (February 2011) (<a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a>)</div></td></tr></tbody></table> The <a href="/wiki/OptimJ" title="OptimJ">OptimJ</a> programming language is an extension of Java 5. As does Java, Optimj provides maps; but OptimJ also provides true associative arrays. Java arrays are indexed with non-negative integers; associative arrays are indexed with any type of key. <div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>String[String] phoneBook = { "Sally Smart" -> "555-9999", "John Doe" -> "555-1212", "J. Random Hacker" -> "553-1337" }; // String[String] is not a java type but an optimj type: // associative array of strings indexed by strings. // iterate over the values for (String number : phoneBook) { System.out.println(number); } // The previous statement prints: "555-9999" "555-1212" "553-1337" // iterate over the keys for (String name : phoneBook.keys) { System.out.println(name + " -> " + phoneBook[name]); } // phoneBook[name] access a value by a key (it looks like java array access) // i.e. phoneBook["John Doe"] returns "555-1212" </pre></div> Of course, it is possible to define multi-dimensional arrays, to mix Java arrays and associative arrays, to mix maps and associative arrays. <div class="mw-highlight mw-highlight-lang-java mw-content-ltr" dir="ltr"><pre>int[String][][double] a; java.util.Map<String[Object], Integer> b; </pre></div> <div class="mw-heading mw-heading3"><h3 id="Perl_5">Perl 5</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=45" title="Edit section: Perl 5">edit</a>]</div> <a href="/wiki/Perl_5" class="mw-redirect" title="Perl 5">Perl 5</a> has built-in, language-level support for associative arrays. Modern Perl refers to associative arrays as hashes; the term associative array is found in older documentation but is considered somewhat archaic. Perl 5 hashes are flat: keys are strings and values are scalars. However, values may be <a href="/wiki/Reference_(computer_science)" title="Reference (computer science)">references</a> to arrays or other hashes, and the standard Perl 5 module Tie::RefHash enables hashes to be used with reference keys. A hash variable is marked by a <code>%</code> <a href="/wiki/Sigil_(computer_programming)" title="Sigil (computer programming)">sigil</a>, to distinguish it from scalar, array, and other data types. A hash literal is a key-value list, with the preferred form using Perl's <code>=></code> token, which is semantically mostly identical to the comma and makes the key-value association clearer: <div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>my %phone_book = ( 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '553-1337', ); </pre></div> Accessing a hash element uses the syntax <code>$hash_name{$key}</code> – the key is surrounded by <a href="/wiki/Bracket#Curly_bracket" title="Bracket">curly braces</a> and the hash name is prefixed by a <code>$</code>, indicating that the hash element itself is a scalar value, even though it is part of a hash. The value of <code>$phone_book{'John Doe'}</code> is <code>'555-1212'</code>. The <code>%</code> sigil is only used when referring to the hash as a whole, such as when asking for <code>keys %phone_book</code>. The list of keys and values can be extracted using the built-in functions <code>keys</code> and <code>values</code>, respectively. So, for example, to print all the keys of a hash: <div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>foreach $name (keys %phone_book) { print $name, "\n"; } </pre></div> One can iterate through (key, value) pairs using the <code>each</code> function: <div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>while (($name, $number) = each %phone_book) { print 'Number for ', $name, ': ', $number, "\n"; } </pre></div> A hash "reference", which is a scalar value that points to a hash, is specified in literal form using curly braces as delimiters, with syntax otherwise similar to specifying a hash literal: <div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>my $phone_book = { 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '553-1337', }; </pre></div> Values in a hash reference are accessed using the dereferencing operator: <div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>print $phone_book->{'Sally Smart'}; </pre></div> When the hash contained in the hash reference needs to be referred to as a whole, as with the <code>keys</code> function, the syntax is as follows: <div class="mw-highlight mw-highlight-lang-perl mw-content-ltr" dir="ltr"><pre>foreach $name (keys %{$phone_book}) { print 'Number for ', $name, ': ', $phone_book->{$name}, "\n"; } </pre></div> <div class="mw-heading mw-heading3"><h3 id="Perl_6_(Raku)">Perl 6 (Raku)</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=46" title="Edit section: Perl 6 (Raku)">edit</a>]</div> <a href="/wiki/Raku_(programming_language)" title="Raku (programming language)">Perl 6</a>, renamed as "Raku", also has built-in, language-level support for associative arrays, which are referred to as hashes or as objects performing the "associative" role. As in Perl 5, Perl 6 default hashes are flat: keys are strings and values are scalars. One can define a hash to not coerce all keys to strings automatically: these are referred to as "object hashes", because the keys of such hashes remain the original object rather than a stringification thereof. A hash variable is typically marked by a <code>%</code> <a href="/wiki/Sigil_(computer_programming)" title="Sigil (computer programming)">sigil</a>, to visually distinguish it from scalar, array, and other data types, and to define its behaviour towards iteration. A hash literal is a key-value list, with the preferred form using Perl's <code>=></code> token, which makes the key-value association clearer: <div class="mw-highlight mw-highlight-lang-perl6 mw-content-ltr" dir="ltr"><pre>my %phone-book = 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '553-1337', ; </pre></div> Accessing a hash element uses the syntax <code>%hash_name{$key}</code> – the key is surrounded by curly braces and the hash name (note that the sigil does not change, contrary to Perl 5). The value of <code>%phone-book{'John Doe'}</code> is <code>'555-1212'</code>. The list of keys and values can be extracted using the built-in functions <code>keys</code> and <code>values</code>, respectively. So, for example, to print all the keys of a hash: <div class="mw-highlight mw-highlight-lang-perl6 mw-content-ltr" dir="ltr"><pre>for %phone-book.keys -> $name { say $name; } </pre></div> By default, when iterating through a hash, one gets key–value pairs. <div class="mw-highlight mw-highlight-lang-perl6 mw-content-ltr" dir="ltr"><pre>for %phone-book -> $entry { say "Number for $entry.key(): $entry.value()"; # using extended interpolation features } </pre></div> It is also possible to get alternating key values and value values by using the <code>kv</code> method: <div class="mw-highlight mw-highlight-lang-perl6 mw-content-ltr" dir="ltr"><pre>for %phone-book.kv -> $name, $number { say "Number for $name: $number"; } </pre></div> Raku doesn't have any references. Hashes can be passed as single parameters that are not flattened. If you want to make sure that a subroutine only accepts hashes, use the % sigil in the Signature. <div class="mw-highlight mw-highlight-lang-perl6 mw-content-ltr" dir="ltr"><pre>sub list-phone-book(%pb) { for %pb.kv -> $name, $number { say "Number for $name: $number"; } } list-phone-book(%phone-book); </pre></div> In compliance with <a href="/wiki/Gradual_typing" title="Gradual typing">gradual typing</a>, hashes may be subjected to type constraints, confining a set of valid keys to a certain type. <div class="mw-highlight mw-highlight-lang-perl6 mw-content-ltr" dir="ltr"><pre># Define a hash whose keys may only be integer numbers ("Int" type). my %numbersWithNames{Int}; # Keys must be integer numbers, as in this case. %numbersWithNames.push(1 => "one"); # This will cause an error, as strings as keys are invalid. %numbersWithNames.push("key" => "two"); </pre></div> <div class="mw-heading mw-heading3"><h3 id="PHP">PHP</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=47" title="Edit section: PHP">edit</a>]</div> <a href="/wiki/PHP" title="PHP">PHP</a>'s built-in array type is, in reality, an associative array. Even when using numerical indexes, PHP internally stores arrays as associative arrays.<a href="#cite_note-13">[13]</a> So, PHP can have non-consecutively numerically indexed arrays. The keys have to be of integer (floating point numbers are truncated to integer) or string type, while values can be of arbitrary types, including other arrays and objects. The arrays are heterogeneous: a single array can have keys of different types. PHP's associative arrays can be used to represent trees, lists, stacks, queues, and other common data structures not built into PHP. An associative array can be declared using the following syntax: <div class="mw-highlight mw-highlight-lang-php mw-content-ltr" dir="ltr"><pre>$phonebook = array(); $phonebook['Sally Smart'] = '555-9999'; $phonebook['John Doe'] = '555-1212'; $phonebook['J. Random Hacker'] = '555-1337'; // or $phonebook = array( 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '555-1337', ); // or, as of PHP 5.4 $phonebook = [ 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '555-1337', ]; // or $phonebook['contacts']['Sally Smart']['number'] = '555-9999'; $phonebook['contacts']['John Doe']['number'] = '555-1212'; $phonebook['contacts']['J. Random Hacker']['number'] = '555-1337'; </pre></div> PHP can loop through an associative array as follows: <div class="mw-highlight mw-highlight-lang-php mw-content-ltr" dir="ltr"><pre>foreach ($phonebook as $name => $number) { echo 'Number for ', $name, ': ', $number, "\n"; } // For the last array example it is used like this foreach ($phonebook['contacts'] as $name => $num) { echo 'Name: ', $name, ', number: ', $num['number'], "\n"; } </pre></div> PHP has an extensive set of functions to operate on arrays.<a href="#cite_note-14">[14]</a> Associative arrays that can use objects as keys, instead of strings and integers, can be implemented with the <code>SplObjectStorage</code> class from the Standard PHP Library (SPL).<a href="#cite_note-15">[15]</a> <div class="mw-heading mw-heading3"><h3 id="Pike">Pike</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=48" title="Edit section: Pike">edit</a>]</div> <a href="/wiki/Pike_(programming_language)" title="Pike (programming language)">Pike</a> has built-in support for associative arrays, which are referred to as mappings. Mappings are created as follows: <div class="mw-highlight mw-highlight-lang-pike mw-content-ltr" dir="ltr"><pre>mapping(string:string) phonebook = ([ "Sally Smart":"555-9999", "John Doe":"555-1212", "J. Random Hacker":"555-1337" ]); </pre></div> Accessing and testing for presence in mappings is done using the indexing operator. So <code>phonebook["Sally Smart"]</code> would return the string <code>"555-9999"</code>, and <code>phonebook["John Smith"]</code> would return 0. Iterating through a mapping can be done using <code>foreach</code>: <div class="mw-highlight mw-highlight-lang-pike mw-content-ltr" dir="ltr"><pre>foreach(phonebook; string key; string value) { write("%s:%s\n", key, value); } </pre></div> Or using an iterator object: <div class="mw-highlight mw-highlight-lang-pike mw-content-ltr" dir="ltr"><pre>Mapping.Iterator i = get_iterator(phonebook); while (i->index()) { write("%s:%s\n", i->index(), i->value()); i->next(); } </pre></div> Elements of a mapping can be removed using <code>m_delete</code>, which returns the value of the removed index: <div class="mw-highlight mw-highlight-lang-pike mw-content-ltr" dir="ltr"><pre>string sallys_number = m_delete(phonebook, "Sally Smart"); </pre></div> <div class="mw-heading mw-heading3"><h3 id="PostScript">PostScript</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=49" title="Edit section: PostScript">edit</a>]</div> In <a href="/wiki/PostScript" title="PostScript">PostScript</a>, associative arrays are called dictionaries. In Level 1 PostScript they must be created explicitly, but Level 2 introduced direct declaration using a double-angled-bracket syntax: <div class="mw-highlight mw-highlight-lang-postscript mw-content-ltr" dir="ltr"><pre> % Level 1 declaration 3 dict dup begin /red (rouge) def /green (vert) def /blue (bleu) def end % Level 2 declaration << /red (rot) /green (gruen) /blue (blau) >> % Both methods leave the dictionary on the operand stack </pre></div> Dictionaries can be accessed directly, using <code>get</code>, or implicitly, by placing the dictionary on the dictionary stack using <code>begin</code>: <div class="mw-highlight mw-highlight-lang-postscript mw-content-ltr" dir="ltr"><pre> % With the previous two dictionaries still on the operand stack /red get print % outputs 'rot' begin green print % outputs 'vert' end </pre></div> Dictionary contents can be iterated through using <code>forall</code>, though not in any particular order: <div class="mw-highlight mw-highlight-lang-postscript mw-content-ltr" dir="ltr"><pre> % Level 2 example << /This 1 /That 2 /Other 3 >> {exch =print ( is ) print ==} forall </pre></div> Which may output: <div class="mw-highlight mw-highlight-lang-postscript mw-content-ltr" dir="ltr"><pre> That is 2 This is 1 Other is 3 </pre></div> Dictionaries can be augmented (up to their defined size only in Level 1) or altered using <code>put</code>, and entries can be removed using <code>undef</code>: <div class="mw-highlight mw-highlight-lang-postscript mw-content-ltr" dir="ltr"><pre> % define a dictionary for easy reuse: /MyDict << /rouge (red) /vert (gruen) >> def % add to it MyDict /bleu (blue) put % change it MyDict /vert (green) put % remove something MyDict /rouge undef </pre></div> <div class="mw-heading mw-heading3"><h3 id="Prolog">Prolog</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=50" title="Edit section: Prolog">edit</a>]</div> Some versions of <a href="/wiki/Prolog" title="Prolog">Prolog</a> include dictionary ("dict") utilities.<a href="#cite_note-16">[16]</a> <div class="mw-heading mw-heading3"><h3 id="Python">Python</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=51" title="Edit section: Python">edit</a>]</div> In <a href="/wiki/Python_(programming_language)" title="Python (programming language)">Python</a>, associative arrays are called "<a href="/wiki/Python_syntax_and_semantics#Collection_types" title="Python syntax and semantics">dictionaries</a>". Dictionary literals are delimited by curly braces: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>phonebook = { "Sally Smart": "555-9999", "John Doe": "555-1212", "J. Random Hacker": "553-1337", } </pre></div> Dictionary items can be accessed using the array indexing operator: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>>>> phonebook["Sally Smart"] '555-9999' </pre></div> Loop <a href="/wiki/Iterator#Python" title="Iterator">iterating</a> through all the keys of the dictionary: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>>>> for key in phonebook: ... print(key, phonebook[key]) Sally Smart 555-9999 J. Random Hacker 553-1337 John Doe 555-1212 </pre></div> Iterating through (key, value) tuples: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>>>> for key, value in phonebook.items(): ... print(key, value) Sally Smart 555-9999 J. Random Hacker 553-1337 John Doe 555-1212 </pre></div> Dictionary keys can be individually deleted using the <code>del</code> statement. The corresponding value can be returned before the key-value pair is deleted using the "pop" method of "dict" type: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>>>> del phonebook["John Doe"] >>> val = phonebook.pop("Sally Smart") >>> phonebook.keys() # Only one key left ['J. Random Hacker'] </pre></div> Python 2.7 and 3.x also support <a rel="nofollow" class="external text" href="https://peps.python.org/pep-0274/">dict comprehensions</a> (similar to <a href="/wiki/List_comprehension" title="List comprehension">list comprehensions</a>), a compact syntax for generating a dictionary from any iterator: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>>>> square_dict = {i: i*i for i in range(5)} >>> square_dict {0: 0, 1: 1, 2: 4, 3: 9, 4: 16} >>> {key: value for key, value in phonebook.items() if "J" in key} {'J. Random Hacker': '553-1337', 'John Doe': '555-1212'} </pre></div> Strictly speaking, a dictionary is a super-set of an associative array, since neither the keys or values are limited to a single datatype. One could think of a dictionary as an "associative list" using the nomenclature of Python. For example, the following is also legitimate: <div class="mw-highlight mw-highlight-lang-python mw-content-ltr" dir="ltr"><pre>phonebook = { "Sally Smart": "555-9999", "John Doe": None, "J. Random Hacker": -3.32, 14: "555-3322", } </pre></div> The dictionary keys must be of an <a href="/wiki/Immutable_object" title="Immutable object">immutable</a> data type. In Python, strings are immutable due to their method of implementation. <div class="mw-heading mw-heading3"><h3 id="Red">Red</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=52" title="Edit section: Red">edit</a>]</div> In <a href="/wiki/Red_(programming_language)" title="Red (programming language)">Red</a> the built-in <code>map!</code><a href="#cite_note-17">[17]</a> datatype provides an associative array that maps values of word, string, and scalar key types to values of any type. A hash table is used internally for lookup. A map can be written as a literal, such as <code>#(key1 value1 key2 value2 ...)</code>, or can be created using <code>make map! [key1 value1 key2 value2 ...]</code>: <div class="mw-highlight mw-highlight-lang-red mw-content-ltr" dir="ltr"><pre>Red [Title:"My map"] my-map: make map! [ "Sally Smart" "555-9999" "John Doe" "555-1212" "J. Random Hacker" "553-1337" ] ; Red preserves case for both keys and values, however lookups are case insensitive by default; it is possible to force case sensitivity using the <code>/case</code> refinement for <code>select</code> and <code>put</code>. ; It is of course possible to use <code>word!</code> values as keys, in which case it is generally preferred to use <code>set-word!</code> values when creating the map, but any word type can be used for lookup or creation. my-other-map: make map! [foo: 42 bar: false] ; Notice that the block is not reduced or evaluated in any way, therefore in the above example the key <code>bar</code> is associated with the <code>word!</code> <code>false</code> rather than the <code>logic!</code> value false; literal syntax can be used if the latter is desired: my-other-map: make map! [foo: 42 bar: #[false]] ; or keys can be added after creation: my-other-map: make map! [foo: 42] my-other-map/bar: false ; Lookup can be written using <code>path!</code> notation or using the <code>select</code> action: select my-map "Sally Smart" my-other-map/foo ; You can also loop through all keys and values with <code>foreach</code>: foreach [key value] my-map [ print [key "is associated to" value] ] ; A key can be removed using <code>remove/key</code>: remove/key my-map "Sally Smart" </pre></div> <div class="mw-heading mw-heading3"><h3 id="REXX">REXX</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=53" title="Edit section: REXX">edit</a>]</div> In <a href="/wiki/REXX" class="mw-redirect" title="REXX">REXX</a>, associative arrays are called "stem variables" or "Compound variables". <div class="mw-highlight mw-highlight-lang-rexx mw-content-ltr" dir="ltr"><pre>KEY = 'Sally Smart' PHONEBOOK.KEY = '555-9999' KEY = 'John Doe' PHONEBOOK.KEY = '555-1212' KEY = 'J. Random Hacker' PHONEBOOK.KEY = '553-1337' </pre></div> Stem variables with numeric keys typically start at 1 and go up from there. The 0-key stem variable by convention contains the total number of items in the stem: <div class="mw-highlight mw-highlight-lang-rexx mw-content-ltr" dir="ltr"><pre>NAME.1 = 'Sally Smart' NAME.2 = 'John Doe' NAME.3 = 'J. Random Hacker' NAME.0 = 3 </pre></div> REXX has no easy way of automatically accessing the keys of a stem variable; and typically the keys are stored in a separate associative array, with numeric keys. <div class="mw-heading mw-heading3"><h3 id="Ruby">Ruby</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=54" title="Edit section: Ruby">edit</a>]</div> In <a href="/wiki/Ruby_programming_language" class="mw-redirect" title="Ruby programming language">Ruby</a> a hash table is used as follows: <div class="mw-highlight mw-highlight-lang-rb mw-content-ltr" dir="ltr"><pre>phonebook = { 'Sally Smart' => '555-9999', 'John Doe' => '555-1212', 'J. Random Hacker' => '553-1337' } phonebook['John Doe'] </pre></div> Ruby supports hash looping and iteration with the following syntax: <div class="mw-highlight mw-highlight-lang-irb mw-content-ltr" dir="ltr"><pre>irb(main):007:0> ### iterate over keys and values irb(main):008:0* phonebook.each {|key, value| puts key + " => " + value} Sally Smart => 555-9999 John Doe => 555-1212 J. Random Hacker => 553-1337 => {"Sally Smart"=>"555-9999", "John Doe"=>"555-1212", "J. Random Hacker"=>"553-1337"} irb(main):009:0> ### iterate keys only irb(main):010:0* phonebook.each_key {|key| puts key} Sally Smart John Doe J. Random Hacker => {"Sally Smart"=>"555-9999", "John Doe"=>"555-1212", "J. Random Hacker"=>"553-1337"} irb(main):011:0> ### iterate values only irb(main):012:0* phonebook.each_value {|value| puts value} 555-9999 555-1212 553-1337 => {"Sally Smart"=>"555-9999", "John Doe"=>"555-1212", "J. Random Hacker"=>"553-1337"} </pre></div> Ruby also supports many other useful operations on hashes, such as merging hashes, selecting or rejecting elements that meet some criteria, inverting (swapping the keys and values), and flattening a hash into an array. <div class="mw-heading mw-heading3"><h3 id="Rust">Rust</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=55" title="Edit section: Rust">edit</a>]</div> The <a href="/wiki/Rust_(programming_language)" title="Rust (programming language)">Rust</a> standard library provides a hash map (<code>std::collections::HashMap</code>) and a <a href="/wiki/B-tree" title="B-tree">B-tree</a> map (<code>std::collections::BTreeMap</code>). They share several methods with the same names, but have different requirements for the types of keys that can be inserted. The <code>HashMap</code> requires keys to implement the <code>Eq</code> (<a href="/wiki/Equivalence_relation" title="Equivalence relation">equivalence relation</a>) and <code>Hash</code> (hashability) traits and it stores entries in an unspecified order, and the <code>BTreeMap</code> requires the <code>Ord</code> (<a href="/wiki/Total_order" title="Total order">total order</a>) trait for its keys and it stores entries in an order defined by the key type. The order is reflected by the default iterators. <div class="mw-highlight mw-highlight-lang-rust mw-content-ltr" dir="ltr"><pre>use std::collections::HashMap; let mut phone_book = HashMap::new(); phone_book.insert("Sally Smart", "555-9999"); phone_book.insert("John Doe", "555-1212"); phone_book.insert("J. Random Hacker", "555-1337"); </pre></div> The default iterators visit all entries as tuples. The <code>HashMap</code> iterators visit entries in an unspecified order and the <code>BTreeMap</code> iterator visits entries in the order defined by the key type. <div class="mw-highlight mw-highlight-lang-rust mw-content-ltr" dir="ltr"><pre>for (name, number) in &phone_book { println!("{} {}", name, number); } </pre></div> There is also an iterator for keys: <div class="mw-highlight mw-highlight-lang-rust mw-content-ltr" dir="ltr"><pre>for name in phone_book.keys() { println!("{}", name); } </pre></div> <div class="mw-heading mw-heading3"><h3 id="S-Lang">S-Lang</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=56" title="Edit section: S-Lang">edit</a>]</div> <a href="/wiki/S-Lang" title="S-Lang">S-Lang</a> has an associative array type: <div class="mw-highlight mw-highlight-lang-text mw-content-ltr" dir="ltr"><pre>phonebook = Assoc_Type[]; phonebook["Sally Smart"] = "555-9999" phonebook["John Doe"] = "555-1212" phonebook["J. Random Hacker"] = "555-1337" </pre></div> You can also loop through an associated array in a number of ways: <div class="mw-highlight mw-highlight-lang-text mw-content-ltr" dir="ltr"><pre>foreach name (phonebook) { vmessage ("%s %s", name, phonebook[name]); } </pre></div> To print a sorted-list, it is better to take advantage of S-lang's strong support for standard arrays: <div class="mw-highlight mw-highlight-lang-text mw-content-ltr" dir="ltr"><pre>keys = assoc_get_keys(phonebook); i = array_sort(keys); vals = assoc_get_values(phonebook); array_map (Void_Type, &vmessage, "%s %s", keys[i], vals[i]); </pre></div> <div class="mw-heading mw-heading3"><h3 id="Scala">Scala</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=57" title="Edit section: Scala">edit</a>]</div> <a href="/wiki/Scala_(programming_language)" title="Scala (programming language)">Scala</a> provides an immutable <code>Map</code> class as part of the <code>scala.collection</code> framework: <div class="mw-highlight mw-highlight-lang-scala mw-content-ltr" dir="ltr"><pre>val phonebook = Map("Sally Smart" -> "555-9999", "John Doe" -> "555-1212", "J. Random Hacker" -> "553-1337") </pre></div> Scala's <a href="/wiki/Type_inference" title="Type inference">type inference</a> will decide that this is a <code>Map[String, String]</code>. To access the array: <div class="mw-highlight mw-highlight-lang-scala mw-content-ltr" dir="ltr"><pre>phonebook.get("Sally Smart") </pre></div> This returns an <code>Option</code> type, Scala's equivalent of the <a href="/wiki/Monad_(functional_programming)#The_Maybe_monad" title="Monad (functional programming)">Maybe monad</a> in Haskell. <div class="mw-heading mw-heading3"><h3 id="Smalltalk">Smalltalk</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=58" title="Edit section: Smalltalk">edit</a>]</div> In <a href="/wiki/Smalltalk" title="Smalltalk">Smalltalk</a> a <code>Dictionary</code> is used: <div class="mw-highlight mw-highlight-lang-smalltalk mw-content-ltr" dir="ltr"><pre>phonebook := Dictionary new. phonebook at: 'Sally Smart' put: '555-9999'. phonebook at: 'John Doe' put: '555-1212'. phonebook at: 'J. Random Hacker' put: '553-1337'. </pre></div> To access an entry the message <code>#at:</code> is sent to the dictionary object: <div class="mw-highlight mw-highlight-lang-smalltalk mw-content-ltr" dir="ltr"><pre>phonebook at: 'Sally Smart' </pre></div> Which gives: <div class="mw-highlight mw-highlight-lang-text mw-content-ltr" dir="ltr"><pre> '555-9999' </pre></div> A dictionary hashes, or compares, based on equality and marks both key and value as <a href="/wiki/Garbage_collection_(computer_science)#Strong_and_weak_references" title="Garbage collection (computer science)">strong references</a>. Variants exist in which hash/compare on identity (IdentityDictionary) or keep <a href="/wiki/Garbage_collection_(computer_science)#Strong_and_weak_references" title="Garbage collection (computer science)">weak references</a> (WeakKeyDictionary / WeakValueDictionary). Because every object implements #hash, any object can be used as key (and of course also as value). <div class="mw-heading mw-heading3"><h3 id="SNOBOL">SNOBOL</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=59" title="Edit section: SNOBOL">edit</a>]</div> <a href="/wiki/SNOBOL" title="SNOBOL">SNOBOL</a> is one of the first (if not the first) programming languages to use associative arrays. Associative arrays in SNOBOL are called Tables. <div class="mw-highlight mw-highlight-lang-snobol mw-content-ltr" dir="ltr"><pre>PHONEBOOK = TABLE() PHONEBOOK['Sally Smart'] = '555-9999' PHONEBOOK['John Doe'] = '555-1212' PHONEBOOK['J. Random Hacker'] = '553-1337' </pre></div> <div class="mw-heading mw-heading3"><h3 id="Standard_ML">Standard ML</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=60" title="Edit section: Standard ML">edit</a>]</div> The SML'97 standard of the <a href="/wiki/Standard_ML" title="Standard ML">Standard ML</a> programming language does not provide any associative containers. However, various implementations of Standard ML do provide associative containers. The library of the popular <a href="/wiki/Standard_ML_of_New_Jersey" title="Standard ML of New Jersey">Standard ML of New Jersey</a> (SML/NJ) implementation provides a signature (somewhat like an "interface"), <code>ORD_MAP</code>, which defines a common interface for ordered functional (immutable) associative arrays. There are several general functors—<code>BinaryMapFn</code>, <code>ListMapFn</code>, <code>RedBlackMapFn</code>, and <code>SplayMapFn</code>—that allow you to create the corresponding type of ordered map (the types are a <a href="/wiki/Self-balancing_binary_search_tree" title="Self-balancing binary search tree">self-balancing binary search tree</a>, sorted <a href="/wiki/Association_list" title="Association list">association list</a>, <a href="/wiki/Red%E2%80%93black_tree" title="Red–black tree">red–black tree</a>, and <a href="/wiki/Splay_tree" title="Splay tree">splay tree</a>, respectively) using a user-provided structure to describe the key type and comparator. The functor returns a structure in accordance with the <code>ORD_MAP</code> interface. In addition, there are two pre-defined modules for associative arrays that employ integer keys: <code>IntBinaryMap</code> and <code>IntListMap</code>. <div class="mw-highlight mw-highlight-lang-sml mw-content-ltr" dir="ltr"><pre>- structure StringMap = BinaryMapFn (struct type ord_key = string val compare = String.compare end); structure StringMap : ORD_MAP - val m = StringMap.insert (StringMap.empty, "Sally Smart", "555-9999") val m = StringMap.insert (m, "John Doe", "555-1212") val m = StringMap.insert (m, "J. Random Hacker", "553-1337"); val m = T {cnt=3,key="John Doe", left=T {cnt=1,key="J. Random Hacker",left=E,right=E,value="553-1337"}, right=T {cnt=1,key="Sally Smart",left=E,right=E,value="555-9999"}, value="555-1212"} : string StringMap.map - StringMap.find (m, "John Doe"); val it = SOME "555-1212" : string option </pre></div> SML/NJ also provides a polymorphic hash table: <div class="mw-highlight mw-highlight-lang-sml mw-content-ltr" dir="ltr"><pre>- exception NotFound; exception NotFound - val m : (string, string) HashTable.hash_table = HashTable.mkTable (HashString.hashString, op=) (3, NotFound); val m = HT {eq_pred=fn,hash_fn=fn,n_items=ref 0,not_found=NotFound(-), table=ref [|NIL,NIL,NIL,NIL,NIL,NIL,NIL,NIL,NIL,NIL,NIL,NIL,...|]} : (string,string) HashTable.hash_table - HashTable.insert m ("Sally Smart", "555-9999"); val it = () : unit - HashTable.insert m ("John Doe", "555-1212"); val it = () : unit - HashTable.insert m ("J. Random Hacker", "553-1337"); val it = () : unit HashTable.find m "John Doe"; (* returns NONE if not found *) val it = SOME "555-1212" : string option - HashTable.lookup m "John Doe"; (* raises the exception if not found *) val it = "555-1212" : string </pre></div> Monomorphic hash tables are also supported, using the <code>HashTableFn</code> functor. Another Standard ML implementation, <a href="/wiki/Moscow_ML" class="mw-redirect" title="Moscow ML">Moscow ML</a>, also provides some associative containers. First, it provides polymorphic hash tables in the <code>Polyhash</code> structure. Also, some functional maps from the SML/NJ library above are available as <code>Binarymap</code>, <code>Splaymap</code>, and <code>Intmap</code> structures. <div class="mw-heading mw-heading3"><h3 id="Tcl">Tcl</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=61" title="Edit section: Tcl">edit</a>]</div> There are two <a href="/wiki/Tcl" title="Tcl">Tcl</a> facilities that support associative-array semantics. An "array" is a collection of variables. A "dict" is a full implementation of associative arrays. <div class="mw-heading mw-heading4"><h4 id="array">array</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=62" title="Edit section: array">edit</a>]</div> <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>set {phonebook(Sally Smart)} 555-9999 set john {John Doe} set phonebook($john) 555-1212 set {phonebook(J. Random Hacker)} 553-1337 </pre></div> If there is a space character in the variable name, the name must be grouped using either curly brackets (no substitution performed) or double quotes (substitution is performed). Alternatively, several array elements can be set by a single command, by presenting their mappings as a list (words containing whitespace are braced): <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>array set phonebook [list {Sally Smart} 555-9999 {John Doe} 555-1212 {J. Random Hacker} 553-1337] </pre></div> To access one array entry and put it to standard output: <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>puts $phonebook(Sally\ Smart) </pre></div> Which returns this result: <div class="mw-highlight mw-highlight-lang-text mw-content-ltr" dir="ltr"><pre>555-9999 </pre></div> To retrieve the entire array as a dictionary: <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>array get phonebook </pre></div> The result can be (order of keys is unspecified, not because the dictionary is unordered, but because the array is): <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>{Sally Smart} 555-9999 {J. Random Hacker} 553-1337 {John Doe} 555-1212 </pre></div> <div class="mw-heading mw-heading4"><h4 id="dict">dict</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=63" title="Edit section: dict">edit</a>]</div> <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>set phonebook [dict create {Sally Smart} 555-9999 {John Doe} 555-1212 {J. Random Hacker} 553-1337] </pre></div> To look up an item: <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>dict get $phonebook {John Doe} </pre></div> To iterate through a dict: <div class="mw-highlight mw-highlight-lang-tcl mw-content-ltr" dir="ltr"><pre>foreach {name number} $phonebook { puts "name: $name\nnumber: $number" } </pre></div> <div class="mw-heading mw-heading3"><h3 id="Visual_Basic">Visual Basic</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=64" title="Edit section: Visual Basic">edit</a>]</div> <a href="/wiki/Visual_Basic" title="Visual Basic">Visual Basic</a> can use the Dictionary class from the <a href="/wiki/Windows_Scripting_Host" class="mw-redirect" title="Windows Scripting Host">Microsoft Scripting Runtime</a> (which is shipped with Visual Basic 6). There is no standard implementation common to all versions: <div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>' Requires a reference to SCRRUN.DLL in Project Properties Dim phoneBook As New Dictionary phoneBook.Add "Sally Smart", "555-9999" phoneBook.Item("John Doe") = "555-1212" phoneBook("J. Random Hacker") = "553-1337" For Each name In phoneBook MsgBox name & " = " & phoneBook(name) Next </pre></div> <div class="mw-heading mw-heading3"><h3 id="Visual_Basic_.NET">Visual Basic .NET</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=65" title="Edit section: Visual Basic .NET">edit</a>]</div> <a href="/wiki/Visual_Basic_.NET" class="mw-redirect" title="Visual Basic .NET">Visual Basic .NET</a> uses the collection classes provided by the <a href="/wiki/.NET_Framework" title=".NET Framework">.NET Framework</a>. <div class="mw-heading mw-heading4"><h4 id="Creation_5">Creation</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=66" title="Edit section: Creation">edit</a>]</div> The following code demonstrates the creation and population of a dictionary (see <a href="#C#">the C# example on this page</a> for additional information): <div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>Dim dic As New System.Collections.Generic.Dictionary(Of String, String) dic.Add("Sally Smart", "555-9999") dic("John Doe") = "555-1212" dic.Item("J. Random Hacker") = "553-1337" </pre></div> An alternate syntax would be to use a collection initializer, which compiles down to individual calls to <code>Add</code>: <div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>Dim dic As New System.Collections.Dictionary(Of String, String) From { {"Sally Smart", "555-9999"}, {"John Doe", "555-1212"}, {"J. Random Hacker", "553-1337"} } </pre></div> <div class="mw-heading mw-heading4"><h4 id="Access_by_key_5">Access by key</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=67" title="Edit section: Access by key">edit</a>]</div> Example demonstrating access (see <a href="#C#_access">C# access</a>): <div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>Dim sallyNumber = dic("Sally Smart") ' or Dim sallyNumber = dic.Item("Sally Smart") </pre></div> <div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>Dim result As String = Nothing Dim sallyNumber = If(dic.TryGetValue("Sally Smart", result), result, "n/a") </pre></div> <div class="mw-heading mw-heading4"><h4 id="Enumeration_4">Enumeration</h4>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=68" title="Edit section: Enumeration">edit</a>]</div> Example demonstrating enumeration (see <a href="#C#_enumeration">#C# enumeration</a>): <div class="mw-highlight mw-highlight-lang-vbnet mw-content-ltr" dir="ltr"><pre>' loop through the collection and display each entry. For Each kvp As KeyValuePair(Of String, String) In dic Console.WriteLine("Phone number for {0} is {1}", kvp.Key, kvp.Value) Next </pre></div> <div class="mw-heading mw-heading3"><h3 id="Windows_PowerShell">Windows PowerShell</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=69" title="Edit section: Windows PowerShell">edit</a>]</div> Unlike many other <a href="/wiki/Command_line_interpreter" class="mw-redirect" title="Command line interpreter">command line interpreters</a>, <a href="/wiki/Windows_PowerShell" class="mw-redirect" title="Windows PowerShell">Windows PowerShell</a> has built-in, language-level support for defining associative arrays: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$phonebook = @{ 'Sally Smart' = '555-9999'; 'John Doe' = '555-1212'; 'J. Random Hacker' = '553-1337' } </pre></div> As in JavaScript, if the property name is a valid identifier, the quotes can be omitted: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$myOtherObject = @{ foo = 42; bar = $false } </pre></div> Entries can be separated by either a semicolon or a newline: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$myOtherObject = @{ foo = 42 bar = $false ; zaz = 3 } </pre></div> Keys and values can be any <a href="/wiki/.NET_Framework" title=".NET Framework">.NET</a> object type: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$now = [DateTime]::Now $tomorrow = $now.AddDays(1) $ProcessDeletionSchedule = @{ (Get-Process notepad) = $now (Get-Process calc) = $tomorrow } </pre></div> It is also possible to create an empty associative array and add single entries, or even other associative arrays, to it later on: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$phonebook = @{} $phonebook += @{ 'Sally Smart' = '555-9999' } $phonebook += @{ 'John Doe' = '555-1212'; 'J. Random Hacker' = '553-1337' } </pre></div> New entries can also be added by using the array index operator, the property operator, or the <code>Add()</code> method of the underlying .NET object: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$phonebook = @{} $phonebook['Sally Smart'] = '555-9999' $phonebook.'John Doe' = '555-1212' $phonebook.Add('J. Random Hacker', '553-1337') </pre></div> To dereference assigned objects, the array index operator, the property operator, or the parameterized property <code>Item()</code> of the .NET object can be used: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$phonebook['Sally Smart'] $phonebook.'John Doe' $phonebook.Item('J. Random Hacker') </pre></div> You can loop through an associative array as follows: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$phonebook.Keys | foreach { "Number for {0}: {1}" -f $_,$phonebook.$_ } </pre></div> An entry can be removed using the <code>Remove()</code> method of the underlying .NET object: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$phonebook.Remove('Sally Smart') </pre></div> Hash tables can be added: <div class="mw-highlight mw-highlight-lang-powershell mw-content-ltr" dir="ltr"><pre>$hash1 = @{ a=1; b=2 } $hash2 = @{ c=3; d=4 } $hash3 = $hash1 + $hash2 </pre></div> <div class="mw-heading mw-heading2"><h2 id="Data_serialization_formats_support">Data serialization formats support</h2>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=70" title="Edit section: Data serialization formats support">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1251242444"><table class="box-Expand_section plainlinks metadata ambox mbox-small-left ambox-content" role="presentation"><tbody><tr><td class="mbox-image"><a href="/wiki/File:Wiki_letter_w_cropped.svg" class="mw-file-description"><img alt="[icon]" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/20px-Wiki_letter_w_cropped.svg.png" decoding="async" width="20" height="14" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/30px-Wiki_letter_w_cropped.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Wiki_letter_w_cropped.svg/40px-Wiki_letter_w_cropped.svg.png 2x" data-file-width="44" data-file-height="31" /></a></td><td class="mbox-text"><div class="mbox-text-span">This section needs expansion. You can help by <a class="external text" href="https://en.wikipedia.org/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=">adding to it</a>. (September 2010)</div></td></tr></tbody></table> Many data serialization formats also support associative arrays (see <a href="/wiki/Comparison_of_data_serialization_formats#Syntax_comparison_of_human-readable_formats" class="mw-redirect" title="Comparison of data serialization formats">this table</a>) <div class="mw-heading mw-heading3"><h3 id="JSON">JSON</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=71" title="Edit section: JSON">edit</a>]</div> In <a href="/wiki/JSON" title="JSON">JSON</a>, associative arrays are also referred to as objects. Keys can only be strings. <div class="mw-highlight mw-highlight-lang-javascript mw-content-ltr" dir="ltr"><pre>{ "Sally Smart": "555-9999", "John Doe": "555-1212", "J. Random Hacker": "555-1337" } </pre></div> <div class="mw-heading mw-heading3"><h3 id="YAML">YAML</h3>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=72" title="Edit section: YAML">edit</a>]</div> <a href="/wiki/YAML" title="YAML">YAML</a> associative arrays are also called map elements or key-value pairs. YAML places no restrictions on the types of keys; in particular, they are not restricted to being scalar or string values. <div class="mw-highlight mw-highlight-lang-yaml mw-content-ltr" dir="ltr"><pre>Sally Smart: 555-9999 John Doe: 555-1212 J. Random Hacker: 555-1337 </pre></div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=Comparison_of_programming_languages_(associative_array)&action=edit&section=73" title="Edit section: References">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width reflist-columns-2"> <ol class="references"> <li id="cite_note-1"><a href="#cite_ref-1">^</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20071015024120/http://www.cl.cam.ac.uk/~cwc22/hashtable/">here</a>, archived <a rel="nofollow" class="external text" href="https://web.archive.org/web/20040902160534/http://www.cl.cam.ac.uk/~cwc22/hashtable/">here</a>, with the source code available <a rel="nofollow" class="external text" href="https://github.com/davidar/c-hashtable/">here</a>. <a href="/wiki/POSIX" title="POSIX">POSIX</a> 1003.1-2001 describes the functions <code>hcreate()</code>, <code>hdestroy()</code> and <code>hsearch()</code> </li> <li id="cite_note-2"><a href="#cite_ref-2">^</a> <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://uthash.sourceforge.net/">"uthash: a hash table for C structures"</a>. 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