def to_numpy_(self, table_name: str="data") -> numpy.array:
        """Convert the main dataframe to a numpy array

        :param table_name: name of the python variable, defaults to "data"
        :param table_name: str, optional
        :return: a numpy array
        :rtype: np.array

        :example: ``ds.to_numpy_("myvar")``
        """
        try:
            renderer = pytablewriter.NumpyTableWriter
            data = self._build_export(renderer, table_name)
            return data
        except Exception as e:
            self.err(e, "Can not convert data to numpy array")