public function getRange($key, $length) {
        $badKeys = [];

        for ($i = 0; $i < $key; $i++) {
            array_push($badKeys, $i);
        }

        for ($i = $key + $length; $i < count($this->_datas); $i++) {
            array_push($badKeys, $i);
        }

        return array_diff_key($this->_datas, array_flip($badKeys));
    }