BUG: df.groupby().aggregate() doesn't preserve subclass type

[jaredight]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

pandas as pd

class MySeries(pd.Series):
    pass

class MyDataFrame(pd.DataFrame):
    @property
    def _constructor(self):
        return MyDataFrame
    _constructor_sliced = MySeries

MySeries._constructor_expanddim = MyDataFrame

df = MyDataFrame({"a": reversed(range(10)), "b": list('aaaabbbccc')})

assert isinstance(df.groupby("b").agg({"a": "sum"}), MyDataFrame)

Traceback

AssertionError                            Traceback (most recent call last)
<ipython-input-7-e355635bac0a> in <cell line: 14>()
     12 df = MyDataFrame({"a": reversed(range(10)), "b": list('aaaabbbccc')})
     13 
---> 14 assert isinstance(df.groupby("b").agg({"a": "sum"}), MyDataFrame)

AssertionError: 

Issue Description

The df.groupby().agg() operation does not preserve subclass type. See this StackOverflow question for more details.

Other relevant issues:

• groupby and resample methods do not preserve subclassed data structures #28330
• BUG: DataFrameSubClass.groupby() doesn't use methods of subclass #51757

Expected Behavior

Expected behavior is that df.groupby().agg() would be the same class type as df.

Installed Versions

INSTALLED VERSIONS

commit : d9cdd2e
python : 3.10.12.final.0
python-bits : 64
OS : Linux
OS-release : 6.1.85+
Version : #1 SMP PREEMPT_DYNAMIC Thu Jun 27 21:05:47 UTC 2024
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : en_US.UTF-8
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.2.2
numpy : 1.26.4
pytz : 2024.1
dateutil : 2.8.2
setuptools : 71.0.4
pip : 24.1.2
Cython : 3.0.11
pytest : 7.4.4
hypothesis : None
sphinx : 5.0.2
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.9.4
html5lib : 1.1
pymysql : None
psycopg2 : 2.9.9
jinja2 : 3.1.4
IPython : 7.34.0
pandas_datareader : 0.10.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2024.6.1
gcsfs : 2024.6.1
matplotlib : 3.7.1
numba : 0.60.0
numexpr : 2.10.1
odfpy : None
openpyxl : 3.1.5
pandas_gbq : 0.23.1
pyarrow : 14.0.2
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.13.1
sqlalchemy : 2.0.32
tables : 3.8.0
tabulate : 0.9.0
xarray : 2024.6.0
xlrd : 2.0.1
zstandard : None
tzdata : 2024.1
qtpy : None
pyqt5 : None

[AshmitGupta]

take

[rhshadrach]

@jaredight - you get the desired behavior by overriding _constructor and _constructor_expanddim in MySeries. See here:

https://pandas.pydata.org/docs/development/extending.html#override-constructor-properties

[mroeschke]

Thanks for the report but as explained this is supported with the correct overrides so closing