Save DataFrame as csv.

        Parameters
        ----------
        filepath : str
        sep : str, optional
            Separator used between values.
        header : bool, optional
            Whether to save the header.
        index : bool, optional
            Whether to save the index columns.

        Returns
        -------
        None

def to_csv(self, filepath, sep=',', header=True, index=True):
        """Save DataFrame as csv.

        Parameters
        ----------
        filepath : str
        sep : str, optional
            Separator used between values.
        header : bool, optional
            Whether to save the header.
        index : bool, optional
            Whether to save the index columns.

        Returns
        -------
        None

        """
        from ..io import to_csv

        return to_csv(self, filepath, sep=sep, header=header, index=index)