Support for use of Enums in MultiIndex

ci/appveyor-27.yaml

@@ -27,3 +27,4 @@ dependencies:
   - pytest
   - pytest-xdist
   - moto
+  - enum34

ci/circle-27-compat.yaml

@@ -22,6 +22,7 @@ dependencies:
   # universal
   - pytest
   - pytest-xdist
+  - enum34
   - pip:
     - html5lib==1.0b2
     - beautifulsoup4==4.2.1

ci/travis-27-locale.yaml

@@ -22,6 +22,7 @@ dependencies:
   # universal
   - pytest
   - pytest-xdist
+  - enum34
   - pip:
     - html5lib==1.0b2
     - beautifulsoup4==4.2.1

ci/travis-27.yaml

@@ -42,6 +42,7 @@ dependencies:
   - pytest
   - pytest-xdist
   - moto
+  - enum34
   - pip:
     - backports.lzma
     - cpplint

doc/source/whatsnew/v0.23.1.txt

@@ -88,6 +88,7 @@ Indexing
 - Bug in :meth:`MultiIndex.set_names` where error raised for a ``MultiIndex`` with ``nlevels == 1`` (:issue:`21149`)
 - Bug in :class:`IntervalIndex` constructors where creating an ``IntervalIndex`` from categorical data was not fully supported (:issue:`21243`, issue:`21253`)
 - Bug in :meth:`MultiIndex.sort_index` which was not guaranteed to sort correctly with ``level=1``; this was also causing data misalignment in particular :meth:`DataFrame.stack` operations (:issue:`20994`, :issue:`20945`, :issue:`21052`)
+- Bug in :func:`pandas.core.arrays.categorical._factorize_from_iterable` inappropriately caused ``TypeError`` to be raised when an ``Enum`` was used as a factor in a ``MultiIndex`` (:issue:`21298`)
 -
 
 I/O

pandas/core/arrays/categorical.py

@@ -2523,7 +2523,7 @@ def _factorize_from_iterable(values):
                                       ordered=values.ordered)
         codes = values.codes
     else:
-        cat = Categorical(values, ordered=True)
+        cat = Categorical(values, ordered=False)
         categories = cat.categories
         codes = cat.codes
     return codes, categories

pandas/tests/indexes/test_multi.py

@@ -3307,3 +3307,39 @@ def test_duplicate_multiindex_labels(self):
         with pytest.raises(ValueError):
             ind.set_levels([['A', 'B', 'A', 'A', 'B'], [2, 1, 3, -2, 5]],
                            inplace=True)
+
+    def test_use_enum_in_multiindex(self):
+        # GH 21298
+        # Allow use of Enums as one of the factors in a MultiIndex.
+        from enum import Enum
+        from pandas.core.algorithms import take_1d
+
+        # See https://github.com/pandas-dev/pandas/blob/
+        # 0c65c57a279e755ab7093db925d1e580f9878dae/pandas/util/testing.py#L793-L799.
+        # We cannot simply use tm.assert_index_equal, as the "expected" index
+        # cannot actually be built yet.
+        def _get_ilevel_values(index, level):
+            # accept level number only
+            unique = index.levels[level]
+            labels = index.labels[level]
+            filled = take_1d(
+                unique.values,
+                labels, fill_value=unique._na_value
+            )
+            values = unique._shallow_copy(filled, name=index.names[level])
+            return values
+
+        MyEnum = Enum("MyEnum", "A B")
+        df = pd.DataFrame(columns=pd.MultiIndex.from_product(iterables=[
+            MyEnum,
+            [1, 2]
+        ]))
+        exp_index_0 = pd.Index([MyEnum.A, MyEnum.A, MyEnum.B, MyEnum.B],
+                               dtype='object')
+        tm.assert_index_equal(_get_ilevel_values(df.columns, 0), exp_index_0)
+
+        expected = df.copy()
+        df = df.append({(MyEnum.A, 1): "abc", (MyEnum.B, 2): "xyz"},
+                       ignore_index=True)
+        expected.loc[0, [(MyEnum.A, 1), (MyEnum.B, 2)]] = 'abc', 'xyz'
+        tm.assert_frame_equal(df, expected)