convertToSingleArray

    /**
     * recursive function in order to convert a multiple dimensions array to a single dimension array
     * @param array $array
     * @param array $res
     * @return $res
     * @auther pzzrudlf <pzzrudlf@gmail.com>
     */
    public function convertToSingleArray($array, &$res=[])
    {
        foreach ($array as $key => $value) {
            array_push($res,$key);
            self::convertToSingleArray($value, $res);
        }
        return $res;
    }