def mapping(self):
return (<EOL>self._user_id_mapping,<EOL>self._user_feature_mapping,<EOL>self._item_id_mapping,<EOL>self._item_feature_mapping,<EOL>)<EOL>
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