BUG: Preserve categorical dtypes in MultiIndex levels (#13743) by pijucha · Pull Request #13854 · pandas-dev/pandas (original) (raw)

Other places where a categorical dtype is lost in similar circumstances.

cidx = pd.CategoricalIndex(['y', 'x'], categories=list("xyz"), ordered=True) cidx_nonunique = pd.CategoricalIndex(['y', 'x', 'y'], categories=list("xyz"), ordered=True)

1. concat
   df = pd.DataFrame([[10, 11, 12]])
   pd.concat([df, df], keys=cidx).index.levels[0]
   Out[32]: Index(['y', 'x'], dtype='object')
2. stack with a non-unique index/multi-index:
   df = pd.DataFrame([[10, 11, 12]], columns=cidx_nonunique)
   df.stack().index.levels[1]
   Out[35]: Index(['x', 'y', 'z'], dtype='object')
3. get_dummies
   pd.get_dummies(cidx).columns
   Out[36]: Index(['x', 'y', 'z'], dtype='object')
4. make_axis_dummies with transform
   df = pd.DataFrame([[10, 11]], columns=cidx)
   ldf = pd.Panel({'A': df, 'B': df}).to_frame()
   pd.core.reshape.make_axis_dummies(panel.to_frame(), transform=lambda x: x).columns
   Out[53]: Index(['x', 'y', 'z'], dtype='object')
5. panel_index
   pi = pd.core.panel.panel_index([0, 1, 2], cidx)
   pi.levels[1]
   Out[57]: Index(['x', 'y'], dtype='object', name='panel')
6. pytables: LegacyTable.read()
   No quick example yet.