Description
Pandas version checks
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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
import numpy as np
print(pd.show_versions())
df_normal = pd.DataFrame({"x": ["a", "b", "b", np.nan]})
print(df_normal, end="\n\n")
print(df_normal.groupby("x", dropna=False).size(), end="\n\n")
df_categorical = pd.DataFrame({"x": ["a", "b", "b", np.nan]}).astype(
{"x": pd.CategoricalDtype()}
)
print(df_categorical, end="\n\n")
print(df_categorical.groupby("x", dropna=False).size(), end="\n\n")Issue Description
Although dropna=False, pandas drops the NA in the categorical column. This can be seen because it has not shown up in the produced series.
If the data type is not categorical, the groupby correctly keeps the NA in the column, as shown by df_normal
Expected Behavior
- Pandas does not drop the NA in the categorical column in the groupby when dropna=False
- The normal and the categorical DataFrame function the same
Installed Versions
INSTALLED VERSIONS
commit : ca60aab
python : 3.9.13.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19043
machine : AMD64
processor : Intel64 Family 6 Model 94 Stepping 3, GenuineIntel
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : English_United Kingdom.1252
pandas : 1.4.4
numpy : 1.23.3
pytz : 2022.2.1
dateutil : 2.8.2
setuptools : 58.1.0
pip : 22.0.4
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
markupsafe : 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
None