List::Util - A selection of general-utility list subroutines

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The subroutines defined are</p> <dl> <dt id="first-BLOCK-LIST"><a class="permalink" href="#first-BLOCK-LIST">#</a><a id="first"></a>first BLOCK LIST</dt> <dd> <p>Similar to <code>grep</code> in that it evaluates BLOCK setting <code>$_</code> to each element of LIST in turn. <code>first</code> returns the first element where the result from BLOCK is a true value. If BLOCK never returns true or LIST was empty then <code>undef</code> is returned.</p> <pre><code>$foo = first { defined($_) } @list # first defined value in @list $foo = first { $_ > $value } @list # first value in @list which # is greater than $value</code></pre> <p>This function could be implemented using <code>reduce</code> like this</p> <pre><code>$foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list</code></pre> <p>for example wanted() could be defined() which would return the first defined value in @list</p> </dd> <dt id="max-LIST"><a class="permalink" href="#max-LIST">#</a><a id="max"></a>max LIST</dt> <dd> <p>Returns the entry in the list with the highest numerical value. If the list is empty then <code>undef</code> is returned.</p> <pre><code>$foo = max 1..10 # 10 $foo = max 3,9,12 # 12 $foo = max @bar, @baz # whatever</code></pre> <p>This function could be implemented using <code>reduce</code> like this</p> <pre><code>$foo = reduce { $a > $b ? $a : $b } 1..10</code></pre> </dd> <dt id="maxstr-LIST"><a class="permalink" href="#maxstr-LIST">#</a><a id="maxstr"></a>maxstr LIST</dt> <dd> <p>Similar to <code>max</code>, but treats all the entries in the list as strings and returns the highest string as defined by the <code>gt</code> operator. If the list is empty then <code>undef</code> is returned.</p> <pre><code>$foo = maxstr 'A'..'Z' # 'Z' $foo = maxstr "hello","world" # "world" $foo = maxstr @bar, @baz # whatever</code></pre> <p>This function could be implemented using <code>reduce</code> like this</p> <pre><code>$foo = reduce { $a gt $b ? $a : $b } 'A'..'Z'</code></pre> </dd> <dt id="min-LIST"><a class="permalink" href="#min-LIST">#</a><a id="min"></a>min LIST</dt> <dd> <p>Similar to <code>max</code> but returns the entry in the list with the lowest numerical value. If the list is empty then <code>undef</code> is returned.</p> <pre><code>$foo = min 1..10 # 1 $foo = min 3,9,12 # 3 $foo = min @bar, @baz # whatever</code></pre> <p>This function could be implemented using <code>reduce</code> like this</p> <pre><code>$foo = reduce { $a < $b ? $a : $b } 1..10</code></pre> </dd> <dt id="minstr-LIST"><a class="permalink" href="#minstr-LIST">#</a><a id="minstr"></a>minstr LIST</dt> <dd> <p>Similar to <code>min</code>, but treats all the entries in the list as strings and returns the lowest string as defined by the <code>lt</code> operator. If the list is empty then <code>undef</code> is returned.</p> <pre><code>$foo = minstr 'A'..'Z' # 'A' $foo = minstr "hello","world" # "hello" $foo = minstr @bar, @baz # whatever</code></pre> <p>This function could be implemented using <code>reduce</code> like this</p> <pre><code>$foo = reduce { $a lt $b ? $a : $b } 'A'..'Z'</code></pre> </dd> <dt id="reduce-BLOCK-LIST"><a class="permalink" href="#reduce-BLOCK-LIST">#</a><a id="reduce"></a>reduce BLOCK LIST</dt> <dd> <p>Reduces LIST by calling BLOCK, in a scalar context, multiple times, setting <code>$a</code> and <code>$b</code> each time. The first call will be with <code>$a</code> and <code>$b</code> set to the first two elements of the list, subsequent calls will be done by setting <code>$a</code> to the result of the previous call and <code>$b</code> to the next element in the list.</p> <p>Returns the result of the last call to BLOCK. If LIST is empty then <code>undef</code> is returned. If LIST only contains one element then that element is returned and BLOCK is not executed.</p> <pre><code>$foo = reduce { $a < $b ? $a : $b } 1..10 # min $foo = reduce { $a lt $b ? $a : $b } 'aa'..'zz' # minstr $foo = reduce { $a + $b } 1 .. 10 # sum $foo = reduce { $a . $b } @bar # concat</code></pre> <p>If your algorithm requires that <code>reduce</code> produce an identity value, then make sure that you always pass that identity value as the first argument to prevent <code>undef</code> being returned</p> <pre><code>$foo = reduce { $a + $b } 0, @values; # sum with 0 identity value</code></pre> </dd> <dt id="shuffle-LIST"><a class="permalink" href="#shuffle-LIST">#</a><a id="shuffle"></a>shuffle LIST</dt> <dd> <p>Returns the elements of LIST in a random order</p> <pre><code>@cards = shuffle 0..51 # 0..51 in a random order</code></pre> </dd> <dt id="sum-LIST"><a class="permalink" href="#sum-LIST">#</a><a id="sum"></a>sum LIST</dt> <dd> <p>Returns the sum of all the elements in LIST. If LIST is empty then <code>undef</code> is returned.</p> <pre><code>$foo = sum 1..10 # 55 $foo = sum 3,9,12 # 24 $foo = sum @bar, @baz # whatever</code></pre> <p>This function could be implemented using <code>reduce</code> like this</p> <pre><code>$foo = reduce { $a + $b } 1..10</code></pre> <p>If your algorithm requires that <code>sum</code> produce an identity of 0, then make sure that you always pass <code>0</code> as the first argument to prevent <code>undef</code> being returned</p> <pre><code>$foo = sum 0, @values;</code></pre> </dd> </dl> <h1 id="KNOWN-BUGS"><a class="permalink" href="#KNOWN-BUGS">#</a><a id="KNOWN"></a>KNOWN BUGS</h1> <p>With perl versions prior to 5.005 there are some cases where reduce will return an incorrect result. This will show up as test 7 of reduce.t failing.</p> <h1 id="SUGGESTED-ADDITIONS"><a class="permalink" href="#SUGGESTED-ADDITIONS">#</a><a id="SUGGESTED"></a>SUGGESTED ADDITIONS</h1> <p>The following are additions that have been requested, but I have been reluctant to add due to them being very simple to implement in perl</p> <pre><code># One argument is true sub any { $_ && return 1 for @_; 0 } # All arguments are true sub all { $_ || return 0 for @_; 1 } # All arguments are false sub none { $_ && return 0 for @_; 1 } # One argument is false sub notall { $_ || return 1 for @_; 0 } # How many elements are true sub true { scalar grep { $_ } @_ } # How many elements are false sub false { scalar grep { !$_ } @_ }</code></pre> <h1 id="SEE-ALSO"><a class="permalink" href="#SEE-ALSO">#</a><a id="SEE"></a>SEE ALSO</h1> <p><a href="/5.12.4/Scalar::Util">Scalar::Util</a>, <a href="/5.12.4/List::MoreUtils">List::MoreUtils</a></p> <h1 id="COPYRIGHT"><a class="permalink" href="#COPYRIGHT">#</a>COPYRIGHT</h1> <p>Copyright (c) 1997-2007 Graham Barr <gbarr@pobox.com>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.</p> </div> <div id="footer"> <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p> <p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. Please contact them via the <a href="https://github.com/Perl/perl5/issues">Perl issue tracker</a>, the <a href="https://lists.perl.org/list/perl5-porters.html">mailing list</a>, or <a href="https://kiwiirc.com/client/irc.perl.org/p5p">IRC</a> to report any issues with the contents or format of the documentation.</p> </div> </div> <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.slim.min.js" integrity="sha512-/DXTXr6nQodMUiq+IUJYCt2PPOUjrHJ9wFrqpJ3XkgPNOZVfMok7cRw6CSxyCQxXn6ozlESsSh1/sMCTF1rL/g==" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.1/umd/popper.min.js" integrity="sha512-ubuT8Z88WxezgSqf3RLuNi5lmjstiJcyezx34yIU2gAHonIi27Na7atqzUZCOoY4CExaoFumzOsFQ2Ch+I/HCw==" crossorigin="anonymous"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV" crossorigin="anonymous"></script> <script src="/js/highlight.pack.js"></script> <script>hljs.highlightAll();</script> </body> </html>

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List::Util - A selection of general-utility list subroutines - Perldoc Browser