Return the constructed mappings.

        Invert these to map internal indices to external ids.

        Returns
        -------

        (user id map, user feature map, item id map, item id map): tuple of dictionaries

def mapping(self):
        """
        Return the constructed mappings.

        Invert these to map internal indices to external ids.

        Returns
        -------

        (user id map, user feature map, item id map, item id map): tuple of dictionaries
        """

        return (
            self._user_id_mapping,
            self._user_feature_mapping,
            self._item_id_mapping,
            self._item_feature_mapping,
        )