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  <refentry id="function.array-reduce">
   <refnamediv>
    <refname>array_reduce</refname>
    <refpurpose>
     Iteratively reduce the array to a single value using a callback
     function
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>mixed</type><methodname>array_reduce</methodname>
      <methodparam><type>array</type><parameter>input</parameter></methodparam>
      <methodparam><type>callback</type><parameter>function</parameter></methodparam>
      <methodparam choice="opt"><type>int</type><parameter>initial</parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>array_reduce</function> applies iteratively the
     <parameter>function</parameter> function to the elements of the
     array <parameter>input</parameter>, so as to reduce the array to
     a single value. If the optional <parameter>initial</parameter> is
     available, it will be used at the beginning of the process, or as
     a final result in case the array is empty.
    </para>
    <para>
     <example>
      <title><function>array_reduce</function> example</title>
      <programlisting role="php">
<![CDATA[
<?php
function rsum($v, $w) {
    $v += $w;
    return $v;
}

function rmul($v, $w) {
    $v *= $w;
    return $v;
}

$a = array(1, 2, 3, 4, 5);
$x = array();
$b = array_reduce($a, "rsum");
$c = array_reduce($a, "rmul", 10);
$d = array_reduce($x, "rsum", 1);
?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     This will result in <varname>$b</varname> containing
     <literal>15</literal>, <varname>$c</varname> containing
     <literal>1200</literal> (= 1*2*3*4*5*10), and
     <varname>$d</varname> containing <literal>1</literal>.
    </para>
    <para>
     See also <function>array_filter</function>,
     <function>array_map</function>,
     <function>array_unique</function>, and
     <function>array_count_values</function>.
    </para>
   </refsect1>
  </refentry>

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