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# 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().

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