Returns a copy of the 'row_sparse' parameter on the same context as row_id's.
        The copy only retains rows whose ids occur in provided row ids.
        The parameter must have been initialized on this context before.

        Parameters
        ----------
        row_id: NDArray
            Row ids to retain for the 'row_sparse' parameter.

        Returns
        -------
        NDArray on row_id's context

def row_sparse_data(self, row_id):
        """Returns a copy of the 'row_sparse' parameter on the same context as row_id's.
        The copy only retains rows whose ids occur in provided row ids.
        The parameter must have been initialized on this context before.

        Parameters
        ----------
        row_id: NDArray
            Row ids to retain for the 'row_sparse' parameter.

        Returns
        -------
        NDArray on row_id's context
        """
        if self._stype != 'row_sparse':
            raise RuntimeError("Cannot return a copy of Parameter %s via row_sparse_data() " \
                               "because its storage type is %s. Please use data() instead." \
                               %(self.name, self._stype))
        return self._get_row_sparse(self._data, row_id.context, row_id)