From 27cc0e20e88a1608eadb83de2af9713c081f8d92 Mon Sep 17 00:00:00 2001
From: AshmitGupta <67188586+AshmitGupta@users.noreply.github.com>
Date: Sat, 31 Aug 2024 22:18:58 -0700
Subject: [PATCH 1/3] FIX: Preserve DataFrame subclass type in groupby().agg()

---
 pandas/core/groupby/generic.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index c112d9b6a4b54..f65d721b8ae77 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -1585,6 +1585,9 @@ def aggregate(self, func=None, *args, engine=None, engine_kwargs=None, **kwargs)
             result = self._insert_inaxis_grouper(result)
             result.index = default_index(len(result))
 
+        if isinstance(self.obj, type(self.obj)):
+            result = self.obj._constructor(result)
+
         return result
 
     agg = aggregate

From 14de84b240aff6a660f5b354b8f74701b5bf1051 Mon Sep 17 00:00:00 2001
From: AshmitGupta <67188586+AshmitGupta@users.noreply.github.com>
Date: Sat, 31 Aug 2024 23:18:56 -0700
Subject: [PATCH 2/3] Added tests and whats new

---
 doc/source/whatsnew/v2.3.0.rst       |  2 +-
 pandas/tests/groupby/test_groupby.py | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.3.0.rst b/doc/source/whatsnew/v2.3.0.rst
index 8a64aa7c609d6..d49985882f500 100644
--- a/doc/source/whatsnew/v2.3.0.rst
+++ b/doc/source/whatsnew/v2.3.0.rst
@@ -142,7 +142,7 @@ Plotting
 
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^
--
+- Bug in :meth:`DataFrame.groupby` followed by :meth:`DataFrameGroupBy.agg` not preserving subclass type of the original DataFrame (:issue:`59667`)
 -
 
 Reshaping
diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index 11b874d0b1608..54df1bdb3ffd3 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -3004,6 +3004,30 @@ def test_groupby_agg_namedagg_with_duplicate_columns():
 
     tm.assert_frame_equal(result, expected)
 
+class MyDataFrame(DataFrame):
+    @property
+    def _constructor(self):
+        return MyDataFrame
+
+@pytest.mark.parametrize("data, agg_dict, expected", [
+    pytest.param(
+        {"A": [1, 1, 2, 2], "B": [1, 2, 3, 4]},
+        {"B": "sum"},
+        DataFrame({"B": [3, 7]}, index=Index([1, 2], name="A"))
+    ),
+    pytest.param(
+        {"A": [1, 1, 2, 2], "B": [1, 2, 3, 4], "C": [4, 3, 2, 1]},
+        {"B": "sum", "C": "mean"},
+        DataFrame({"B": [3, 7], "C": [3.5, 1.5]}, index=Index([1, 2], name="A"))
+    ),
+])
+def test_groupby_agg_preserves_subclass(data, agg_dict, expected):
+    # GH#59667
+    df = MyDataFrame(data)
+    result = df.groupby("A").agg(agg_dict)
+    
+    assert isinstance(result, MyDataFrame)
+    tm.assert_frame_equal(result, expected)
 
 def test_groupby_multi_index_codes():
     # GH#54347

From 208d2fced0120fa7cffb42dcddda5fc2c294e035 Mon Sep 17 00:00:00 2001
From: AshmitGupta <67188586+AshmitGupta@users.noreply.github.com>
Date: Sun, 1 Sep 2024 01:48:13 -0700
Subject: [PATCH 3/3] Code style chore (Pre-commit hook)

---
 pandas/tests/groupby/test_groupby.py | 32 +++++++++++++++++-----------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/pandas/tests/groupby/test_groupby.py b/pandas/tests/groupby/test_groupby.py
index 54df1bdb3ffd3..9adc817324a21 100644
--- a/pandas/tests/groupby/test_groupby.py
+++ b/pandas/tests/groupby/test_groupby.py
@@ -3004,31 +3004,37 @@ def test_groupby_agg_namedagg_with_duplicate_columns():
 
     tm.assert_frame_equal(result, expected)
 
+
 class MyDataFrame(DataFrame):
     @property
     def _constructor(self):
         return MyDataFrame
 
-@pytest.mark.parametrize("data, agg_dict, expected", [
-    pytest.param(
-        {"A": [1, 1, 2, 2], "B": [1, 2, 3, 4]},
-        {"B": "sum"},
-        DataFrame({"B": [3, 7]}, index=Index([1, 2], name="A"))
-    ),
-    pytest.param(
-        {"A": [1, 1, 2, 2], "B": [1, 2, 3, 4], "C": [4, 3, 2, 1]},
-        {"B": "sum", "C": "mean"},
-        DataFrame({"B": [3, 7], "C": [3.5, 1.5]}, index=Index([1, 2], name="A"))
-    ),
-])
+
+@pytest.mark.parametrize(
+    "data, agg_dict, expected",
+    [
+        pytest.param(
+            {"A": [1, 1, 2, 2], "B": [1, 2, 3, 4]},
+            {"B": "sum"},
+            DataFrame({"B": [3, 7]}, index=Index([1, 2], name="A")),
+        ),
+        pytest.param(
+            {"A": [1, 1, 2, 2], "B": [1, 2, 3, 4], "C": [4, 3, 2, 1]},
+            {"B": "sum", "C": "mean"},
+            DataFrame({"B": [3, 7], "C": [3.5, 1.5]}, index=Index([1, 2], name="A")),
+        ),
+    ],
+)
 def test_groupby_agg_preserves_subclass(data, agg_dict, expected):
     # GH#59667
     df = MyDataFrame(data)
     result = df.groupby("A").agg(agg_dict)
-    
+
     assert isinstance(result, MyDataFrame)
     tm.assert_frame_equal(result, expected)
 
+
 def test_groupby_multi_index_codes():
     # GH#54347
     df = DataFrame(