BUG: pivot_table someitmes returns Series (pandas-dev#4386)

BUG: pivot_table sometimes returns Series (pandas-dev#4386)

BUG: pivot_table sometimes returns Series (pandas-dev#4386)

Author: mroeschke

pandas/tools/pivot.py

@@ -78,7 +78,6 @@ def pivot_table(data, values=None, index=None, columns=None, aggfunc='mean',
     """
     index = _convert_by(index)
     columns = _convert_by(columns)
-
     if isinstance(aggfunc, list):
         pieces = []
         keys = []
@@ -164,7 +163,8 @@ def pivot_table(data, values=None, index=None, columns=None, aggfunc='mean',
                              margins_name=margins_name)
 
     # discard the top level
-    if values_passed and not values_multi and not table.empty:
+    if values_passed and not values_multi and not table.empty and \
+        (table.columns.nlevels > 1):
         table = table[values[0]]
 
     if len(index) == 0 and len(columns) > 0:

pandas/tools/tests/test_pivot.py

@@ -350,13 +350,13 @@ def _check_output(result, values_col, index=['A', 'B'],
         # no rows
         rtable = self.data.pivot_table(columns=['AA', 'BB'], margins=True,
                                        aggfunc=np.mean)
-        tm.assertIsInstance(rtable, DataFrame)
-
-        table = self.data.pivot_table(index=['AA', 'BB'], margins=True,
-                                      aggfunc='mean')
-        for item in ['DD', 'EE', 'FF']:
-            totals = table.loc[('All', ''), item]
-            self.assertEqual(totals, self.data[item].mean())
+        expected = self.data.groupby(['AA','BB']).mean()
+        expected.loc[('All', ''), :] = self.data[['DD', 'EE', 'FF']].mean()
+        expected = (expected.stack()
+                            .unstack(['BB', 'AA'])
+                            .stack(['AA', 'BB'])
+                            .to_frame())
+        tm.assert_frame_equal(expected, rtable)
 
         # issue number #8349: pivot_table with margins and dictionary aggfunc
         data = [
@@ -485,8 +485,11 @@ def test_margins_no_values_no_cols(self):
         # Regression test on pivot table: no values or cols passed.
         result = self.data[['A', 'B']].pivot_table(
             index=['A', 'B'], aggfunc=len, margins=True)
-        result_list = result.values.flatten().tolist()
-        self.assertEqual(sum(result_list[:-1]), result_list[-1])
+        expected = self.data[['A', 'B']].groupby(['A', 'B']).apply(len)
+        expected.loc[('All', '')] = expected.sum()
+        expected = expected.to_frame()
+
+        tm.assert_frame_equal(result, expected)
 
     def test_margins_no_values_two_rows(self):
         # Regression test on pivot table: no values passed but rows are a