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

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.uasort" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>uasort</refname>
  <refpurpose>Sort an array with a user-defined comparison function and maintain index association</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>uasort</methodname>
   <methodparam><type>array</type><parameter role="reference">array</parameter></methodparam>
   <methodparam><type>callable</type><parameter>value_compare_func</parameter></methodparam>
  </methodsynopsis>
  <para>
   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.
  </para>
  <para>
   This is used mainly when sorting associative arrays where the actual
   element order is significant.
  </para>
  &note.sort-unstable;
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>array</parameter></term>
     <listitem>
      <para>
       The input array.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>value_compare_func</parameter></term>
     <listitem>
      <para>
       See <function>usort</function> and <function>uksort</function> for
       examples of user-defined comparison functions.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   &return.success;
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Basic <function>uasort</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// Comparison function
function cmp($a, $b) {
    if ($a == $b) {
        return 0;
    }
    return ($a < $b) ? -1 : 1;
}

// Array to be sorted
$array = array('a' => 4, 'b' => 8, 'c' => -1, 'd' => -9, 'e' => 2, 'f' => 5, 'g' => 3, 'h' => -4);
print_r($array);

// Sort and print the resulting array
uasort($array, 'cmp');
print_r($array);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
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
)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>usort</function></member>
    <member>&seealso.array.sorting;</member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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