private function dataToJson($data)
        {
            $cols = $this->getColumns($data);

            $rows = [];

            foreach ($data as $key => $row) {
                if ($key != 0 || !$this->_skipFirstRow) {
                    $c = [];

                    foreach ($row as $v) {
                        $c[] = ['v' => $v];
                    }

                    $rows[] = ['c' => $c];
                }
            }

            return json_encode(['cols' => $cols, 'rows' => $rows]);
        }