util.html

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<?xml version="1.0" ?>
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<title>List::Util - A selection of general-utility list subroutines</title>
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<h1><a>List::Util - A selection of general-utility list subroutines</a></h1>
<p><a name="__index__"></a></p>

<!-- INDEX BEGIN -->

<ul>

	<li><a href="#name">NAME</a></li>
	<li><a href="#synopsis">SYNOPSIS</a></li>
	<li><a href="#description">DESCRIPTION</a></li>
	<li><a href="#known_bugs">KNOWN BUGS</a></li>
	<li><a href="#suggested_additions">SUGGESTED ADDITIONS</a></li>
	<li><a href="#copyright">COPYRIGHT</a></li>
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<p>
</p>
<h1><a name="name">NAME</a></h1>
<p>List::Util - A selection of general-utility list subroutines</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
    <span class="keyword">use</span> <span class="variable">List::Util</span> <span class="string">qw(first max maxstr min minstr reduce shuffle sum)</span><span class="operator">;</span>
</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p><code>List::Util</code> contains a selection of subroutines that people have
expressed would be nice to have in the perl core, but the usage would
not really be high enough to warrant the use of a keyword, and the size
so small such that being individual extensions would be wasteful.</p>
<p>By default <code>List::Util</code> does not export any subroutines. The
subroutines defined are</p>
<dl>
<dt><strong><a name="item_first">first BLOCK LIST</a></strong>

<dd>
<p>Similar to <a href="../../lib/Pod/perlfunc.html#item_grep"><code>grep</code></a> in that it evaluates BLOCK setting <a href="../../lib/Pod/perlvar.html#item___"><code>$_</code></a> to each element
of LIST in turn. <a href="#item_first"><code>first</code></a> returns the first element where the result from
BLOCK is a true value. If BLOCK never returns true or LIST was empty then
<a href="../../lib/Pod/perlfunc.html#item_undef"><code>undef</code></a> is returned.</p>
</dd>
<dd>
<pre>
    <span class="variable">$foo</span> <span class="operator">=</span> <span class="variable">first</span> <span class="operator">{</span> <span class="keyword">defined</span><span class="operator">(</span><span class="variable">$_</span><span class="operator">)</span> <span class="operator">}</span> <span class="variable">@list</span>    <span class="comment"># first defined value in @list</span>
    <span class="variable">$foo</span> <span class="operator">=</span> <span class="variable">first</span> <span class="operator">{</span> <span class="variable">$_</span> <span class="operator">&gt;</span> <span class="variable">$value</span> <span class="operator">}</span> <span class="variable">@list</span>    <span class="comment"># first value in @list which</span>
                                          <span class="comment"># is greater than $value</span>
</pre>
</dd>
<dd>
<p>This function could be implemented using <a href="#item_reduce"><code>reduce</code></a> like this</p>
</dd>
<dd>
<pre>
    <span class="variable">$foo</span> <span class="operator">=</span> <span class="variable">reduce</span> <span class="operator">{</span> <span class="keyword">defined</span><span class="operator">(</span><span class="variable">$a</span><span class="operator">)</span> <span class="operator">?</span> <span class="variable">$a</span> <span class="operator">:</span> <span class="variable">wanted</span><span class="operator">(</span><span class="variable">$b</span><span class="operator">)</span> <span class="operator">?</span> <span class="variable">$b</span> <span class="operator">:</span> <span class="keyword">undef</span> <span class="operator">}</span> <span class="keyword">undef</span><span class="operator">,</span> <span class="variable">@list</span>
</pre>
</dd>
<dd>
<p>for example <code>wanted()</code> could be <a href="../../lib/Pod/perlfunc.html#item_defined"><code>defined()</code></a> which would return the first
defined value in @list</p>
</dd>
</li>
<dt><strong><a name="item_max">max LIST</a></strong>

<dd>
<p>Returns the entry in the list with the highest numerical value. If the
list is empty then <a href="../../lib/Pod/perlfunc.html#item_undef"><code>undef</code></a> is returned.</p>
</dd>
<dd>
<pre>
    $foo = max 1..10                # 10
    $foo = max 3,9,12               # 12
    $foo = max @bar, @baz           # whatever</pre>
</dd>
<dd>
<p>This function could be implemented using <a href="#item_reduce"><code>reduce</code></a> like this</p>
</dd>
<dd>
<pre>
    <span class="variable">$foo</span> <span class="operator">=</span> <span class="variable">reduce</span> <span class="operator">{</span> <span class="variable">$a</span> <span class="operator">&gt;</span> <span class="variable">$b</span> <span class="operator">?</span> <span class="variable">$a</span> <span class="operator">:</span> <span class="variable">$b</span> <span class="operator">}</span> <span class="number">1</span><span class="operator">..</span><span class="number">10</span>
</pre>
</dd>
</li>
<dt><strong><a name="item_maxstr">maxstr LIST</a></strong>

<dd>
<p>Similar to <a href="#item_max"><code>max</code></a>, 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 <a href="../../lib/Pod/perlfunc.html#item_undef"><code>undef</code></a> is returned.</p>
</dd>
<dd>
<pre>
    $foo = maxstr 'A'..'Z'          # 'Z'
    $foo = maxstr &quot;hello&quot;,&quot;world&quot;   # &quot;world&quot;
    $foo = maxstr @bar, @baz        # whatever</pre>
</dd>
<dd>
<p>This function could be implemented using <a href="#item_reduce"><code>reduce</code></a> like this</p>
</dd>
<dd>
<pre>
    <span class="variable">$foo</span> <span class="operator">=</span> <span class="variable">reduce</span> <span class="operator">{</span> <span class="variable">$a</span> <span class="keyword">gt</span> <span class="variable">$b</span> <span class="operator">?</span> <span class="variable">$a</span> <span class="operator">:</span> <span class="variable">$b</span> <span class="operator">}</span> <span class="string">'A'</span><span class="operator">..</span><span class="string">'Z'</span>
</pre>
</dd>
</li>
<dt><strong><a name="item_min">min LIST</a></strong>

<dd>
<p>Similar to <a href="#item_max"><code>max</code></a> but returns the entry in the list with the lowest
numerical value. If the list is empty then <a href="../../lib/Pod/perlfunc.html#item_undef"><code>undef</code></a> is returned.</p>
</dd>
<dd>
<pre>
    $foo = min 1..10                # 1
    $foo = min 3,9,12               # 3
    $foo = min @bar, @baz           # whatever</pre>
</dd>
<dd>
<p>This function could be implemented using <a href="#item_reduce"><code>reduce</code></a> like this</p>
</dd>
<dd>
12

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