Convert multidimensional array to single dimensional using php

Below is the function to convert multidimensional array into single dimensional array.

function array_flatten($array, $x = NULL) {

        if (!is_array($array)) {

            return false;

        }

        $result = array();

        $x = ($x == '') ? 0 : $x;

        foreach ($array as $key => $value) {

            if (is_array($value)) {

                $result = array_merge($result, self::array_flatten($value, $x++));

            } else {

                $result[$x][$key] = $value;

            }

        }

        return $result;

    }