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<title>Sort an array by keys using a user-defined comparison function</title>
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<div class="refnamediv">
<h1 class="refname">uksort</h1>
<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">uksort</span> — <span class="dc-title">Sort an array by keys using a user-defined comparison function</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.uksort-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>uksort</strong></span>
( <span class="methodparam"><span class="type">array</span> <code class="parameter reference">&$array</code></span>
, <span class="methodparam"><span class="type"><a href="language.types.callable.html" class="type callable">callable</a></span> <code class="parameter">$key_compare_func</code></span>
)</div>
<p class="para rdfs-comment">
<span class="function"><strong>uksort()</strong></span> will sort the keys of an array using a
user-supplied comparison function. If the array you wish to sort
needs to be sorted by some non-trivial criteria, you should use
this function.
</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.uksort-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">array</code></dt>
<dd>
<p class="para">
The input array.
</p>
</dd>
<dt>
<code class="parameter">key_compare_func</code></dt>
<dd>
<p class="para">
The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.
Note that before PHP 7.0.0 this integer had to be in the range from -2147483648 to 2147483647.
</p>
<div class="methodsynopsis dc-description"><span class="type">int</span> <span class="methodname"><span class="replaceable">callback</span></span> ( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$a</code></span>, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$b</code></span> )</div>
</dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.uksort-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.uksort-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-6253">
<p><strong>Example #1 <span class="function"><strong>uksort()</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: #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 />{<br /> </span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">preg_replace</span><span style="color: #007700">(</span><span style="color: #DD0000">'@^(a|an|the) @'</span><span style="color: #007700">, </span><span style="color: #DD0000">''</span><span style="color: #007700">, </span><span style="color: #0000BB">$a</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">$b </span><span style="color: #007700">= </span><span style="color: #0000BB">preg_replace</span><span style="color: #007700">(</span><span style="color: #DD0000">'@^(a|an|the) @'</span><span style="color: #007700">, </span><span style="color: #DD0000">''</span><span style="color: #007700">, </span><span style="color: #0000BB">$b</span><span style="color: #007700">);<br /> return </span><span style="color: #0000BB">strcasecmp</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 />}<br /><br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= array(</span><span style="color: #DD0000">"John" </span><span style="color: #007700">=> </span><span style="color: #0000BB">1</span><span style="color: #007700">, </span><span style="color: #DD0000">"the Earth" </span><span style="color: #007700">=> </span><span style="color: #0000BB">2</span><span style="color: #007700">, </span><span style="color: #DD0000">"an apple" </span><span style="color: #007700">=> </span><span style="color: #0000BB">3</span><span style="color: #007700">, </span><span style="color: #DD0000">"a banana" </span><span style="color: #007700">=> </span><span style="color: #0000BB">4</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">uksort</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">, </span><span style="color: #DD0000">"cmp"</span><span style="color: #007700">);<br /><br />foreach (</span><span style="color: #0000BB">$a </span><span style="color: #007700">as </span><span style="color: #0000BB">$key </span><span style="color: #007700">=> </span><span style="color: #0000BB">$value</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"</span><span style="color: #0000BB">$key</span><span style="color: #DD0000">: </span><span style="color: #0000BB">$value</span><span style="color: #DD0000">\n"</span><span style="color: #007700">;<br />}<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>
an apple: 3
a banana: 4
the Earth: 2
John: 1
</pre></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.uksort-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>
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