BUG: get_group fails when multi-grouping with a categorical

doc/source/whatsnew/v0.16.2.txt

@@ -68,7 +68,9 @@ Bug Fixes
 - Bug in getting timezone data with ``dateutil`` on various platforms ( :issue:`9059`, :issue:`8639`, :issue:`9663`, :issue:`10121`)
 - Bug in display datetimes with mixed frequencies uniformly; display 'ms' datetimes to the proper precision. (:issue:`10170`)
 
-- Bung in ``Series`` arithmetic methods may incorrectly hold names (:issue:`10068`)
+- Bug in ``Series`` arithmetic methods may incorrectly hold names (:issue:`10068`)
+
+- Bug in ``GroupBy.get_group`` when grouping on multiple keys, one of which is categorical. (:issue:`10132`)
 
 - Bug in ``DatetimeIndex`` and ``TimedeltaIndex`` names are lost after timedelta arithmetics ( :issue:`9926`)
 

pandas/core/index.py

@@ -2964,6 +2964,10 @@ def values(self):
         """ return the underlying data, which is a Categorical """
         return self._data
 
+    def get_values(self):
+        """ return the underlying data as an ndarray """
+        return self._data.get_values()
+
     @property
     def codes(self):
         return self._data.codes

pandas/tests/test_groupby.py

@@ -5140,6 +5140,13 @@ def test_groupby_categorical_two_columns(self):
                          "ints": [1,2,1,2,1,2]}).set_index(["cat","ints"])
         tm.assert_frame_equal(res, exp)
 
+        # GH 10132
+        for key in [('a', 1), ('b', 2), ('b', 1), ('a', 2)]:
+            c, i = key
+            result = groups_double_key.get_group(key)
+            expected = test[(test.cat == c) & (test.ints == i)]
+            assert_frame_equal(result, expected)
+
         d = {'C1': [3, 3, 4, 5], 'C2': [1, 2, 3, 4], 'C3': [10, 100, 200, 34]}
         test = pd.DataFrame(d)
         values = pd.cut(test['C1'], [1, 2, 3, 6])