From 394fcad6753762a9d7eb08d4fba7cdd921581537 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <patrick_hoefler@gmx.net>
Date: Fri, 9 Feb 2024 22:40:03 +0100
Subject: [PATCH] REGR: Fix regression when grouping over a Series

---
 doc/source/whatsnew/v2.2.1.rst         |  1 +
 pandas/core/internals/managers.py      |  5 ++---
 pandas/tests/copy_view/test_methods.py | 11 +++++++++++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.1.rst b/doc/source/whatsnew/v2.2.1.rst
index 883627bd4b19b..51223803403b1 100644
--- a/doc/source/whatsnew/v2.2.1.rst
+++ b/doc/source/whatsnew/v2.2.1.rst
@@ -17,6 +17,7 @@ Fixed regressions
 - Fixed performance regression in :meth:`Series.combine_first` (:issue:`55845`)
 - Fixed regression in :func:`merge_ordered` raising ``TypeError`` for ``fill_method="ffill"`` and ``how="left"`` (:issue:`57010`)
 - Fixed regression in :func:`wide_to_long` raising an ``AttributeError`` for string columns (:issue:`57066`)
+- Fixed regression in :meth:`DataFrame.groupby` raising ``ValueError`` when grouping by a :class:`Series` in some cases (:issue:`57276`)
 - Fixed regression in :meth:`DataFrame.loc` raising ``IndexError`` for non-unique, masked dtype indexes where result has more than 10,000 rows (:issue:`57027`)
 - Fixed regression in :meth:`DataFrame.sort_index` not producing a stable sort for a index with duplicates (:issue:`57151`)
 - Fixed regression in :meth:`DataFrame.to_dict` with ``orient='list'`` and datetime or timedelta types returning integers (:issue:`54824`)
diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
index e077a530d5c1c..f3b3278bb9daf 100644
--- a/pandas/core/internals/managers.py
+++ b/pandas/core/internals/managers.py
@@ -15,7 +15,6 @@
     final,
 )
 import warnings
-import weakref
 
 import numpy as np
 
@@ -339,8 +338,8 @@ def references_same_values(self, mgr: BaseBlockManager, blkno: int) -> bool:
         Checks if two blocks from two different block managers reference the
         same underlying values.
         """
-        ref = weakref.ref(self.blocks[blkno])
-        return ref in mgr.blocks[blkno].refs.referenced_blocks
+        blk = self.blocks[blkno]
+        return any(blk is ref() for ref in mgr.blocks[blkno].refs.referenced_blocks)
 
     def get_dtypes(self) -> npt.NDArray[np.object_]:
         dtypes = np.array([blk.dtype for blk in self.blocks], dtype=object)
diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
index e885a1f0048e9..356b31a82f5ff 100644
--- a/pandas/tests/copy_view/test_methods.py
+++ b/pandas/tests/copy_view/test_methods.py
@@ -273,6 +273,17 @@ def test_reset_index_series_drop(using_copy_on_write, index):
     tm.assert_series_equal(ser, ser_orig)
 
 
+def test_groupby_column_index_in_references():
+    df = DataFrame(
+        {"A": ["a", "b", "c", "d"], "B": [1, 2, 3, 4], "C": ["a", "a", "b", "b"]}
+    )
+    df = df.set_index("A")
+    key = df["C"]
+    result = df.groupby(key, observed=True).sum()
+    expected = df.groupby("C", observed=True).sum()
+    tm.assert_frame_equal(result, expected)
+
+
 def test_rename_columns(using_copy_on_write):
     # Case: renaming columns returns a new dataframe
     # + afterwards modifying the result