public function toArray($sheet = 0)
    {
        $arr = array();
        for ($row = 1; $row <= $this->rowcount($sheet); $row++) {
            for ($col = 1; $col <= $this->colcount($sheet); $col++) {
                $arr[$row][$col] = $this->val($row, $col, $sheet);
            }
        }

        return $arr;
    }