flatten multi-dimensional array in PHP

flatten-multi.php

<?php
$multiDim = array(
    array('one', 'two', 'three'),
    array('four', 'five', 'six'),
    );

$flatten = function ($list, $next) use (&$flatten) {
    if (is_array($next)) {
        return array_reduce($next, $flatten, $list);
    }
    array_push($list, $next);
    return $list;
    };
$flat = array_reduce($multiDim, $flatten, array());

print_r( $flat);