BUG: Inconsistent return type for groupby-resample-count · Issue #46826 · pandas-dev/pandas (original) (raw)

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Reproducible Example

import pandas as pd

df1 = pd.DataFrame(index=pd.DatetimeIndex(['2022-1-1 1:00','2022-1-2 1:00','2022-1-2 1:00']), data={'category':['A','A','B']}) res1 = df1.groupby(['category']).resample('1D').size() print(res1)

df2 = pd.DataFrame(index=pd.DatetimeIndex(['2022-1-1 1:00','2022-1-2 1:00','2022-1-2 1:00', '2022-1-1 1:00']),data={'category':['A','A','B','B']})

res2 = df2.groupby(['category']).resample('1D').size() print(res2)

Issue Description

The two dataframes above, df1 and df2, are identical except for one additional data point in df2.

In df1, category A has samples on the first and second day and category B has a sample only on the second day. When I groupby-resample-count I get a Series with multiindex on category and time:

category
A 2022-01-01 1
2022-01-02 1
B 2022-01-02 1

df2 has one additional data point on an existing category and day, so that category B now has a sample on day 1, corresponding to the first time bin in the resample. The return value is now a dataframe with single-index in category and columns corresponding to the time bins:

category
A 1 1
B 1 1

Expected Behavior

I expect res1 and res2 to have the same type: either a multiindex series like res1 or a dataframe like res2.

Installed Versions

INSTALLED VERSIONS

commit : 4bfe3d0
python : 3.8.8.final.0
python-bits : 64
OS : Linux
OS-release : 5.13.0-1021-aws
Version : #23~20.04.2-Ubuntu SMP Thu Mar 31 11:36:15 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.4.2
numpy : 1.20.1
pytz : 2021.3
dateutil : 2.8.2
pip : 21.0.1
setuptools : 58.0.4
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : 1.3.8
lxml.etree : 4.8.0
html5lib : None
pymysql : 1.0.2
psycopg2 : None
jinja2 : 3.1.1
IPython : 7.22.0
pandas_datareader: None
bs4 : 4.9.3
bottleneck : 1.3.4
brotli :
fastparquet : None
fsspec : None
gcsfs : None
markupsafe : 2.0.1
matplotlib : 3.4.3
numba : None
numexpr : 2.8.1
odfpy : None
openpyxl : 3.0.7
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.6.2
snappy : None
sqlalchemy : 1.4.15
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None