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<title>Sort an array with a user-defined comparison function and maintain index association</title>
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</div><hr /><div id="function.uasort" class="refentry">
<div class="refnamediv">
<h1 class="refname">uasort</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">uasort</span> — <span class="dc-title">Sort an array with a user-defined comparison function and maintain index association</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.uasort-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>uasort</strong></span>
( <span class="methodparam"><span class="type">array</span> <code class="parameter reference">&$array</code></span>
, <span class="methodparam"><span class="type"><a href="language.types.callable.html" class="type callable">callable</a></span> <code class="parameter">$value_compare_func</code></span>
)</div>
<p class="para rdfs-comment">
This function sorts an array such that array indices maintain their
correlation with the array elements they are associated with, using a
user-defined comparison function.
</p>
<p class="para">
This is used mainly when sorting associative arrays where the actual
element order is significant.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
If two members compare as equal, their relative order in the sorted array is undefined.
</p>
</p></blockquote>
</div>
<div class="refsect1 parameters" id="refsect1-function.uasort-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">array</code></em></span>
<dd>
<p class="para">
The input array.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">value_compare_func</code></em></span>
<dd>
<p class="para">
See <span class="function"><a href="function.usort.html" class="function">usort()</a></span> and <span class="function"><a href="function.uksort.html" class="function">uksort()</a></span> for
examples of user-defined comparison functions.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.uasort-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns <strong><code>TRUE</code></strong> on success or <strong><code>FALSE</code></strong> on failure.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.uasort-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-5034">
<p><strong>Example #1 Basic <span class="function"><strong>uasort()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Comparison function<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">cmp</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">, </span><span style="color: #0000BB">$b</span><span style="color: #007700">) {<br /> if (</span><span style="color: #0000BB">$a </span><span style="color: #007700">== </span><span style="color: #0000BB">$b</span><span style="color: #007700">) {<br /> return </span><span style="color: #0000BB">0</span><span style="color: #007700">;<br /> }<br /> return (</span><span style="color: #0000BB">$a </span><span style="color: #007700">< </span><span style="color: #0000BB">$b</span><span style="color: #007700">) ? -</span><span style="color: #0000BB">1 </span><span style="color: #007700">: </span><span style="color: #0000BB">1</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #FF8000">// Array to be sorted<br /></span><span style="color: #0000BB">$array </span><span style="color: #007700">= array(</span><span style="color: #DD0000">'a' </span><span style="color: #007700">=> </span><span style="color: #0000BB">4</span><span style="color: #007700">, </span><span style="color: #DD0000">'b' </span><span style="color: #007700">=> </span><span style="color: #0000BB">8</span><span style="color: #007700">, </span><span style="color: #DD0000">'c' </span><span style="color: #007700">=> -</span><span style="color: #0000BB">1</span><span style="color: #007700">, </span><span style="color: #DD0000">'d' </span><span style="color: #007700">=> -</span><span style="color: #0000BB">9</span><span style="color: #007700">, </span><span style="color: #DD0000">'e' </span><span style="color: #007700">=> </span><span style="color: #0000BB">2</span><span style="color: #007700">, </span><span style="color: #DD0000">'f' </span><span style="color: #007700">=> </span><span style="color: #0000BB">5</span><span style="color: #007700">, </span><span style="color: #DD0000">'g' </span><span style="color: #007700">=> </span><span style="color: #0000BB">3</span><span style="color: #007700">, </span><span style="color: #DD0000">'h' </span><span style="color: #007700">=> -</span><span style="color: #0000BB">4</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Sort and print the resulting array<br /></span><span style="color: #0000BB">uasort</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">, </span><span style="color: #DD0000">'cmp'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
Array
(
[a] => 4
[b] => 8
[c] => -1
[d] => -9
[e] => 2
[f] => 5
[g] => 3
[h] => -4
)
Array
(
[d] => -9
[h] => -4
[c] => -1
[e] => 2
[g] => 3
[a] => 4
[f] => 5
[b] => 8
)
</pre></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.uasort-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.usort.html" class="function" rel="rdfs-seeAlso">usort()</a> - Sort an array by values using a user-defined comparison function</span></li>
<li class="member">The <a href="array.sorting.html" class="link">comparison of array sorting functions</a></li>
</ul>
</p>
</div>
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