BUG: DataFrameGroupBy.transform with axis=1 fails (pandas-dev#36308)

Author: Ethan Chen

pandas/core/groupby/generic.py

@@ -1676,7 +1676,13 @@ def _wrap_transformed_output(
         columns.name = self.obj.columns.name
 
         result = self.obj._constructor(indexed_output)
-        result.columns = columns
+
+        if self.axis == 1:
+            result = result.T
+            result.columns = self.obj.columns
+        else:
+            result.columns = columns
+
         result.index = self.obj.index
 
         return result

pandas/core/groupby/groupby.py

@@ -2668,8 +2668,8 @@ def pct_change(self, periods=1, fill_method="pad", limit=None, freq=None, axis=0
             fill_method = "pad"
             limit = 0
         filled = getattr(self, fill_method)(limit=limit)
-        fill_grp = filled.groupby(self.grouper.codes)
-        shifted = fill_grp.shift(periods=periods, freq=freq)
+        fill_grp = filled.groupby(self.grouper.codes, axis=self.axis)
+        shifted = fill_grp.shift(periods=periods, freq=freq, axis=self.axis)
         return (filled / shifted) - 1
 
     @Substitution(name="groupby")

pandas/tests/frame/apply/test_frame_transform.py

@@ -27,8 +27,6 @@ def test_transform_groupby_kernel(axis, float_frame, op):
         pytest.xfail("DataFrame.cumcount does not exist")
     if op == "tshift":
         pytest.xfail("Only works on time index and is deprecated")
-    if axis == 1 or axis == "columns":
-        pytest.xfail("GH 36308: groupby.transform with axis=1 is broken")
 
     args = [0.0] if op == "fillna" else []
     if axis == 0 or axis == "index":