def sort_index(self, ascending=True):
        """Sort the index of the DataFrame.

        Currently MultiIndex is not supported since Weld is missing multiple-column sort.

        Note this is an expensive operation (brings all data to Weld).

        Parameters
        ----------
        ascending : bool, optional

        Returns
        -------
        DataFrame
            DataFrame sorted according to the index.

        """
        if isinstance(self.index, MultiIndex):
            raise NotImplementedError('Weld does not yet support sorting on multiple columns')

        return self.sort_values(self.index._gather_names(), ascending)
Sort the index of the DataFrame.

        Currently MultiIndex is not supported since Weld is missing multiple-column sort.

        Note this is an expensive operation (brings all data to Weld).

        Parameters
        ----------
        ascending : bool, optional

        Returns
        -------
        DataFrame
            DataFrame sorted according to the index.