• struct_dict['k'] should return a simple 1D ndarray, not a StructDict
• struct_dict[['a', 'b']] should return a proper StructDict including all additional fields like _keys

both problems are visible in this test: https://travis-ci.org/theislab/scanpy/jobs/227216146#L224

but a test should be added for the second point once the first point is fixed

i would have fixed it, but i don’t have the slightest idea what all the “multicolumn” fields are for. also i don’t believe in too many caches and private fields, they get out of sync too easily. recomputing tiny things is fast, e.g. self._keys could simply be replaced with self.dtype.names