From b356c6a36e8dbee8858d12b00df9ef0ea99fd7b6 Mon Sep 17 00:00:00 2001
From: iofall <50991099+iofall@users.noreply.github.com>
Date: Sun, 15 Jan 2023 23:34:37 +0530
Subject: [PATCH 1/2] Fix .transform(ngroup) for axis=1 grouper

---
 pandas/core/groupby/groupby.py                   | 2 +-
 pandas/tests/groupby/transform/test_transform.py | 4 ----
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 431b23023b094..736c8aafc82e2 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -3369,7 +3369,7 @@ def ngroup(self, ascending: bool = True):
         dtype: int64
         """
         with self._group_selection_context():
-            index = self._selected_obj.index
+            index = self._selected_obj._get_axis(self.axis)
             comp_ids = self.grouper.group_info[0]
 
             dtype: type
diff --git a/pandas/tests/groupby/transform/test_transform.py b/pandas/tests/groupby/transform/test_transform.py
index 528f417ea1039..5dab30c6fd7cc 100644
--- a/pandas/tests/groupby/transform/test_transform.py
+++ b/pandas/tests/groupby/transform/test_transform.py
@@ -164,10 +164,6 @@ def test_transform_broadcast(tsframe, ts):
 def test_transform_axis_1(request, transformation_func):
     # GH 36308
 
-    if transformation_func == "ngroup":
-        msg = "ngroup fails with axis=1: #45986"
-        request.node.add_marker(pytest.mark.xfail(reason=msg))
-
     df = DataFrame({"a": [1, 2], "b": [3, 4], "c": [5, 6]}, index=["x", "y"])
     args = get_groupby_method_args(transformation_func, df)
     result = df.groupby([0, 0, 1], axis=1).transform(transformation_func, *args)

From d7c8a58923a0c7f408e21619e6e06cd655e3f126 Mon Sep 17 00:00:00 2001
From: iofall <50991099+iofall@users.noreply.github.com>
Date: Mon, 23 Jan 2023 23:59:10 +0530
Subject: [PATCH 2/2] Add whatsnew for transform axis-1 ngroup bug fix

---
 doc/source/whatsnew/v2.0.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v2.0.0.rst b/doc/source/whatsnew/v2.0.0.rst
index bbecf3fee01f3..ac41fc8d21aa2 100644
--- a/doc/source/whatsnew/v2.0.0.rst
+++ b/doc/source/whatsnew/v2.0.0.rst
@@ -1098,6 +1098,7 @@ Groupby/resample/rolling
 - Bug in :meth:`.DataFrameGroupBy.transform` and :meth:`.SeriesGroupBy.transform` would raise incorrectly when grouper had ``axis=1`` for ``"idxmin"`` and ``"idxmax"`` arguments (:issue:`45986`)
 - Bug in :class:`.DataFrameGroupBy` would raise when used with an empty DataFrame, categorical grouper, and ``dropna=False`` (:issue:`50634`)
 - Bug in :meth:`.SeriesGroupBy.value_counts` did not respect ``sort=False`` (:issue:`50482`)
+- Bug in :meth:`.DataFrameGroupBy.transform` and :meth:`.SeriesGroupBy.transform` would raise incorrectly when grouper had ``axis=1`` for ``"ngroup"`` argument (:issue:`45986`)
 -
 
 Reshaping