BUG: df.groupby(axis=1).size() returns weird output · Issue #48738 · pandas-dev/pandas (original) (raw)
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
import pandas as pd arrays = [['Falcon', 'Falcon', 'Parrot', 'Parrot'], ['Captive', 'Wild', 'Captive', 'Wild']] index = pd.MultiIndex.from_arrays(arrays, names=('Animal', 'Type')) df = pd.DataFrame({'Max Speed': [390., 350., 30., 20.], 'stuff':[1, 2, 3, 4]}, index=index) print(f'original df:\n{df}\n\n') print(f'groupby1:\n{df.groupby(level=0,axis=1).size()}\n\n') print(f'groupby2:\n{df.T.groupby(level=1,axis=1).size()}\n\n')
simpler case
df = pd.DataFrame( { "col1": [0, 3, 2, 3], "col2": [4, 1, 6, 7], "col3": [3, 8, 2, 10], "col4": [1, 13, 6, 15], "col5": [-4, 5, 6, -7], } ) print(f'simple groupby:\n{df.groupby(axis=1, by=[1, 2, 3, 2, 1]).size()}')
Issue Description
In the example, I think that starting on 1.5, .size() is providing multi-column DataFrame (instead of Series) with all columns equal to each other (and names identical to original df columns).
I wonder if that change is intentional, I sure hope it's not.
Output of the reproducer on pandas 1.5
original df:
Max Speed stuff
Animal Type
Falcon Captive 390.0 1
Wild 350.0 2
Parrot Captive 30.0 3
Wild 20.0 4
groupby1:
Max Speed stuff
Animal Type
Falcon Captive 1 1
Wild 1 1
Parrot Captive 1 1
Wild 1 1
groupby2:
Type Captive Wild
Max Speed 2 2
stuff 2 2
simple groupby:
1 2 3
0 2 2 1
1 2 2 1
2 2 2 1
3 2 2 1
Expected Behavior
Expected output (on pandas 1.4.4)
original df:
Max Speed stuff
Animal Type
Falcon Captive 390.0 1
Wild 350.0 2
Parrot Captive 30.0 3
Wild 20.0 4
groupby1:
Max Speed 1
stuff 1
dtype: int64
groupby2:
Type
Captive 2
Wild 2
dtype: int64
simple groupby:
1 2
2 2
3 1
dtype: int64
Installed Versions
pd.show_versions()
INSTALLED VERSIONS
------------------
commit : 87cfe4e38bafe7300a6003a1d18bd80f3f77c763
python : 3.8.13.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.22000
machine : AMD64
processor : AMD64 Family 25 Model 80 Stepping 0, AuthenticAMD
byteorder : little
LC_ALL : None
LANG : None
LOCALE : Russian_Russia.1251
pandas : 1.5.0
numpy : 1.23.3
pytz : 2022.2.1
dateutil : 2.8.2
setuptools : 65.3.0
pip : 22.2.2
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader: None
bs4 : None
bottleneck : None
brotli : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : None
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : None
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None
tzdata : None