protected function _getColumnKey($column)
    {
        if (!is_array($column)) {
            $matches = $this->_matchColumnString($column);
            $columnKey = $matches[1];
        } elseif (!empty($column['attribute'])) {
            $columnKey = $column['attribute'];
        } elseif (!empty($column['label'])) {
            $columnKey = $column['label'];
        } elseif (!empty($column['header'])) {
            $columnKey = $column['header'];
        } elseif (!empty($column['class'])) {
            $columnKey = $column['class'];
        } else {
            $columnKey = null;
        }
        return hash('crc32', $columnKey);
    }