Function to recursively flatten multidimensional PHP array.

flatten.php

<?php
// Requires PHP 5.3+
// Found here: http://stackoverflow.com/a/1320156

function flatten_array(array $array) {
    $flattened_array = array();
    array_walk_recursive($array, function($a) use (&$flattened_array) { $flattened_array[] = $a; });
    return $flattened_array;
}

@zdenko:

You should include type hinting to avoid possible type errors. Slightly modified:

function flatten(array $arr) {
        return array_reduce($arr, function ($c, $a) { 
		return is_array($a) ? array_merge($c, flatten($a)) : array_merge($c, [$a]);

},
[]); 
    }

@Zenko:
If you pass arguments of a function (using func_get_args() which returns an array) to the function you run into Maxium memory exceeded error. How to fix please.