delete second reindexing in _transform_general

Author: arw2019

pandas/core/groupby/generic.py

@@ -556,9 +556,7 @@ def _transform_general(
             if common_dtype is result.dtype:
                 result = maybe_downcast_numeric(result, self._selected_obj.dtype)
 
-        obj = self._selected_obj.dropna() if self.dropna else self._selected_obj
-        result.name = obj.name
-        result.index = obj.index
+        result.name = self._selected_obj.name
         return result
 
     def _transform_fast(self, result) -> Series:

pandas/tests/groupby/test_grouping.py

@@ -610,33 +610,6 @@ def test_list_grouper_with_nat(self):
         expected = {pd.Timestamp("2011-01-01"): 365}
         tm.assert_dict_equal(result.groups, expected)
 
-    @pytest.mark.parametrize(
-        "func,expected",
-        [
-            (
-                "transform",
-                pd.Series(name=2, dtype=np.float64, index=pd.RangeIndex(0, 0, 1)),
-            ),
-            (
-                "agg",
-                pd.Series(name=2, dtype=np.float64, index=pd.Float64Index([], name=1)),
-            ),
-            (
-                "apply",
-                pd.Series(name=2, dtype=np.float64, index=pd.Float64Index([], name=1)),
-            ),
-        ],
-    )
-    def test_evaluate_with_empty_groups(self, func, expected):
-        # 26208
-        # test transform'ing empty groups
-        # (not testing other agg fns, because they return
-        # different index objects.
-        df = pd.DataFrame({1: [], 2: []})
-        g = df.groupby(1)
-        result = getattr(g[2], func)(lambda x: x)
-        tm.assert_series_equal(result, expected)
-
     def test_groupby_empty(self):
         # https://github.com/pandas-dev/pandas/issues/27190
         s = pd.Series([], name="name", dtype="float64")