# array_reduce

(PHP 4 >= 4.0.5, PHP 5)

array_reduce — Iteratively reduce the array to a single value using a callback function

### Description

mixed array_reduce ( array `$input` , callback `$function` [, int `$initial` ] )

array_reduce() applies iteratively the `function` function to the elements of the array `input` , so as to reduce the array to a single value. If the optional `initial` is available, it will be used at the beginning of the process, or as a final result in case the array is empty. If the array is empty and `initial` is not passed, array_reduce() returns `NULL`.

Example#1 array_reduce() example

`<?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);
?>`

This will result in $b containing 15, $c containing 1200 (= 10*1*2*3*4*5), and $d containing 1.

See also array_filter(), array_map(), array_unique(), and array_count_values().