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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.array-reduce" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>array_reduce</refname>
<refpurpose>Iteratively reduce the array to a single value using a callback function</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>mixed</type><methodname>array_reduce</methodname>
<methodparam><type>array</type><parameter>array</parameter></methodparam>
<methodparam><type>callable</type><parameter>callback</parameter></methodparam>
<methodparam choice="opt"><type>mixed</type><parameter>initial</parameter><initializer>&null;</initializer></methodparam>
</methodsynopsis>
<para>
<function>array_reduce</function> applies iteratively the
<parameter>callback</parameter> function to the elements of the
<parameter>array</parameter>, so as to reduce the array to
a single value.
</para>
</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>callback</parameter></term>
<listitem>
<methodsynopsis>
<type>mixed</type><methodname><replaceable>callback</replaceable></methodname>
<methodparam><type>mixed</type><parameter>carry</parameter></methodparam>
<methodparam><type>mixed</type><parameter>item</parameter></methodparam>
</methodsynopsis>
<variablelist>
<varlistentry>
<term><parameter>carry</parameter></term>
<listitem>
<para>
Holds the return value of the previous iteration; in the case of the
first iteration it instead holds the value of
<parameter>initial</parameter>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>item</parameter></term>
<listitem>
<para>
Holds the value of the current iteration.
</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>initial</parameter></term>
<listitem>
<para>
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>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns the resulting value.
</para>
<para>
If the array is empty and <parameter>initial</parameter> is not passed,
<function>array_reduce</function> returns &null;.
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
&array.changelog.by-ref;
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title><function>array_reduce</function> example</title>
<programlisting role="php">
<![CDATA[
<?php
function sum($carry, $item)
{
$carry += $item;
return $carry;
}
function product($carry, $item)
{
$carry *= $item;
return $carry;
}
$a = array(1, 2, 3, 4, 5);
$x = array();
var_dump(array_reduce($a, "sum")); // int(15)
var_dump(array_reduce($a, "product", 10)); // int(1200), because: 10*1*2*3*4*5
var_dump(array_reduce($x, "sum", "No data to reduce")); // string(17) "No data to reduce"
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>array_filter</function></member>
<member><function>array_map</function></member>
<member><function>array_unique</function></member>
<member><function>array_count_values</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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