php-doc-en/reference/array/functions/uksort.xml

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<refentry xml:id="function.uksort" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>uksort</refname>
  <refpurpose>Sort an array by keys using a user-defined comparison function</refpurpose>
 </refnamediv>
 <refsect1>
  <title>Description</title>
  <methodsynopsis>
   <type>bool</type><methodname>uksort</methodname>
   <methodparam><type>array</type><parameter role="reference">array</parameter></methodparam>
   <methodparam><type>callback</type><parameter>cmp_function</parameter></methodparam>
  </methodsynopsis>
  <para>
   <function>uksort</function> 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.
  </para>
  <para>
   Function <parameter>cmp_function</parameter> should accept two
   parameters which will be filled by pairs of <parameter>array</parameter> keys.
   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.
  </para>
  <para>
   &return.success;
  </para>
  <para>
   <example>
    <title><function>uksort</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
function cmp($a, $b)
{
    $a = ereg_replace('^(a|an|the) ', '', $a);
    $b = ereg_replace('^(a|an|the) ', '', $b);
	return strcasecmp($a, $b);
}

$a = array("John" => 1, "the Earth" => 2, "an apple" => 3, "a banana" => 4);

uksort($a, "cmp");

foreach ($a as $key => $value) {
    echo "$key: $value\n";
}
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
an apple: 3
a banana: 4
the Earth: 2
John: 1
]]>
    </screen>
   </example>
  </para>
  <para>
   See also <function>usort</function>, <function>uasort</function>,
   <function>sort</function>, <function>asort</function>,
   <function>arsort</function>, <function>ksort</function>,
   <function>natsort</function>, and <function>rsort</function>.
  </para>
 </refsect1>
</refentry>

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