PHP Manual
Array Functions
Iteratively reduce the array to a single value using a callback function

array_reduce

(PHP 4 >= 4.0.5, PHP 5, PHP 7, PHP 8)

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

Description

array_reduce(array $array, callable $callback, mixed $initial = null): mixed

array_reduce() applies iteratively the callback function to the elements of the array, so as to reduce the array to a single value.

Parameters

array

The input array.

callback

callback(mixed $carry, mixed $item): mixed

carry: Holds the return value of the previous iteration; in the case of the first iteration it instead holds the value of initial.
item: Holds the value of the current iteration.

initial

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.

Return Values

Returns the resulting value.

If the array is empty and initial is not passed, array_reduce() returns null.

Changelog

Version	Description
8.0.0	If `callback` expects a parameter to be passed by reference, this function will now emit an `E_WARNING`.

Examples

Example #1 array_reduce() example

<?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"
?>