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

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  <refentry id="function.uksort">
   <refnamediv>
    <refname>uksort</refname>
    <refpurpose>
     Sort an array by keys using a user-defined comparison function
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>void</type><methodname>uksort</methodname>
      <methodparam><type>array</type><parameter>array</parameter></methodparam>
      <methodparam><type>callback</type><parameter>cmp_function</parameter></methodparam>
     </methodsynopsis>
    <para>
     This 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>
    <example>
     <title><function>uksort</function> example</title>
     <programlisting role="php">
<![CDATA[
function cmp ($a, $b) {
    if ($a == $b) return 0;
    return ($a > $b) ? -1 : 1;
}

$a = array (4 => "four", 3 => "three", 20 => "twenty", 10 => "ten");

uksort ($a, "cmp");

while (list ($key, $value) = each ($a)) {
    echo "$key: $value\n";
}
]]>
     </programlisting>
    </example>
    <para>
     This example would display:
    </para>
    <para>
     <screen>
<![CDATA[
20: twenty
10: ten
4: four
3: three
]]>
     </screen>
    </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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