BUG: df.reset_index loses tz

Author: sinhrks

doc/source/v0.14.1.txt

@@ -252,7 +252,7 @@ Bug Fixes
 
 - Bug in ``Index.astype(float)`` where it would return an ``object`` dtype
   ``Index`` (:issue:`7464`).
-
+- Bug in ``DataFrame.reset_index`` loses ``tz`` (:issue:`3950`)
 
 
 - Bug in non-monotonic ``Index.union`` may preserve ``name`` incorrectly (:issue:`7458`)

pandas/core/frame.py

@@ -2326,19 +2326,24 @@ def reset_index(self, level=None, drop=False, inplace=False, col_level=0,
         else:
             new_obj = self.copy()
 
-        def _maybe_cast(values, labels=None):
-
-            if values.dtype == np.object_:
-                values = lib.maybe_convert_objects(values)
-
-            # if we have the labels, extract the values with a mask
-            if labels is not None:
-                mask = labels == -1
-                values = values.take(labels)
-                if mask.any():
-                    values, changed = com._maybe_upcast_putmask(
-                        values, mask, np.nan)
-
+        def _maybe_casted_values(index, labels=None):
+            if isinstance(index, PeriodIndex):
+                values = index.asobject
+            elif (isinstance(index, DatetimeIndex) and
+                  index.tz is not None):
+                values = index.asobject
+            else:
+                values = index.values
+                if values.dtype == np.object_:
+                    values = lib.maybe_convert_objects(values)
+
+                # if we have the labels, extract the values with a mask
+                if labels is not None:
+                    mask = labels == -1
+                    values = values.take(labels)
+                    if mask.any():
+                        values, changed = com._maybe_upcast_putmask(values,
+                                                                    mask, np.nan)
             return values
 
         new_index = np.arange(len(new_obj))
@@ -2371,7 +2376,7 @@ def _maybe_cast(values, labels=None):
                             col_name = tuple(name_lst)
 
                     # to ndarray and maybe infer different dtype
-                    level_values = _maybe_cast(lev.values, lab)
+                    level_values = _maybe_casted_values(lev, lab)
                     if level is None or i in level:
                         new_obj.insert(0, col_name, level_values)
 
@@ -2387,13 +2392,7 @@ def _maybe_cast(values, labels=None):
                     lev_num = self.columns._get_level_number(col_level)
                     name_lst[lev_num] = name
                     name = tuple(name_lst)
-            if isinstance(self.index, PeriodIndex):
-                values = self.index.asobject
-            elif (isinstance(self.index, DatetimeIndex) and
-                  self.index.tz is not None):
-                values = self.index.asobject
-            else:
-                values = _maybe_cast(self.index.values)
+            values = _maybe_casted_values(self.index)
             new_obj.insert(0, name, values)
 
         new_obj.index = new_index

pandas/tests/test_frame.py

@@ -2182,6 +2182,20 @@ def test_set_index_cast_datetimeindex(self):
         df.pop('ts')
         assert_frame_equal(df, expected)
 
+        # GH 3950
+        # reset_index with single level
+        for tz in ['UTC', 'Asia/Tokyo', 'US/Eastern']:
+            idx = pd.date_range('1/1/2011', periods=5, freq='D', tz=tz, name='idx')
+            df = pd.DataFrame({'a': range(5), 'b': ['A', 'B', 'C', 'D', 'E']}, index=idx) 
+
+            expected = pd.DataFrame({'idx': [datetime(2011, 1, 1), datetime(2011, 1, 2),
+                                             datetime(2011, 1, 3), datetime(2011, 1, 4),
+                                             datetime(2011, 1, 5)], 
+                                     'a': range(5), 'b': ['A', 'B', 'C', 'D', 'E']},
+                                     columns=['idx', 'a', 'b'])
+            expected['idx'] = expected['idx'].apply(lambda d: pd.Timestamp(d, tz=tz))
+            assert_frame_equal(df.reset_index(), expected)
+
     def test_set_index_multiindexcolumns(self):
         columns = MultiIndex.from_tuples([('foo', 1), ('foo', 2), ('bar', 1)])
         df = DataFrame(np.random.randn(3, 3), columns=columns)

pandas/tests/test_multilevel.py

@@ -2078,6 +2078,46 @@ def test_set_index_datetime(self):
         self.assertTrue(df.index.get_level_values(1).equals(idx2))
         self.assertTrue(df.index.get_level_values(2).equals(idx3))
 
+    def test_reset_index_datetime(self):
+        # GH 3950
+        for tz in ['UTC', 'Asia/Tokyo', 'US/Eastern']:
+            idx1 = pd.date_range('1/1/2011', periods=5, freq='D', tz=tz, name='idx1')
+            idx2 = pd.Index(range(5), name='idx2')
+            idx = pd.MultiIndex.from_arrays([idx1, idx2])
+            df = pd.DataFrame({'a': range(5), 'b': ['A', 'B', 'C', 'D', 'E']}, index=idx) 
+
+            expected = pd.DataFrame({'idx1': [datetime.datetime(2011, 1, 1),
+                                              datetime.datetime(2011, 1, 2),
+                                              datetime.datetime(2011, 1, 3),
+                                              datetime.datetime(2011, 1, 4),
+                                              datetime.datetime(2011, 1, 5)], 
+                                     'idx2': range(5),
+                                     'a': range(5), 'b': ['A', 'B', 'C', 'D', 'E']},
+                                     columns=['idx1', 'idx2', 'a', 'b'])
+            expected['idx1'] = expected['idx1'].apply(lambda d: pd.Timestamp(d, tz=tz))
+            assert_frame_equal(df.reset_index(), expected)
+
+            idx3 = pd.date_range('1/1/2012', periods=5, freq='MS', tz='Europe/Paris', name='idx3')
+            idx = pd.MultiIndex.from_arrays([idx1, idx2, idx3])
+            df = pd.DataFrame({'a': range(5), 'b': ['A', 'B', 'C', 'D', 'E']}, index=idx) 
+
+            expected = pd.DataFrame({'idx1': [datetime.datetime(2011, 1, 1),
+                                              datetime.datetime(2011, 1, 2),
+                                              datetime.datetime(2011, 1, 3),
+                                              datetime.datetime(2011, 1, 4),
+                                              datetime.datetime(2011, 1, 5)], 
+                                     'idx2': range(5),
+                                     'idx3': [datetime.datetime(2012, 1, 1),
+                                              datetime.datetime(2012, 2, 1),
+                                              datetime.datetime(2012, 3, 1),
+                                              datetime.datetime(2012, 4, 1),
+                                              datetime.datetime(2012, 5, 1)], 
+                                     'a': range(5), 'b': ['A', 'B', 'C', 'D', 'E']},
+                                     columns=['idx1', 'idx2', 'idx3', 'a', 'b'])
+            expected['idx1'] = expected['idx1'].apply(lambda d: pd.Timestamp(d, tz=tz))
+            expected['idx3'] = expected['idx3'].apply(lambda d: pd.Timestamp(d, tz='Europe/Paris'))
+            assert_frame_equal(df.reset_index(), expected)
+
     def test_set_index_period(self):
         # GH 6631
         df = DataFrame(np.random.random(6))