Description
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Code Sample, a copy-pastable example
import pandas as pd
df = pd.DataFrame({"a": list("abcde"), "b": list("abcde")}, index=list("aabbc"), dtype="category")
df.agg("-".join, axis=1)Using pandas 1.2.5:
a a-a
a b-b
b c-c
b d-d
c e-e
dtype: object
Using pandas 1.3.0:
a b-b
b d-d
c e-e
dtype: object
It does not look like this is an issue if I use df.apply instead of df.agg.
Problem description
When a aggregation of the rows is run on a dataframe with categorical columns and non-unique indices, the result is the wrong length.
It's weird that the output isn't the right length. Since I'm computing a value per row, I expect the same number of rows in the output as in the input. It's especially weird that this only happens if the columns are categorical.
That is:
df = pd.DataFrame({"a": list("abcde"), "b": list("abcde")}, index=list("aabbc"))
df.agg("-".join, axis=1)a a-a
a b-b
b c-c
b d-d
c e-e
dtype: object
in both versions.
Expected Output
I would expect the same output between versions. The result given by 1.2.5 seems more correct to me at the moment.
Output of pd.show_versions()
INSTALLED VERSIONS
------------------
commit : f00ed8f47020034e752baf0250483053340971b0
python : 3.8.10.final.0
python-bits : 64
OS : Darwin
OS-release : 20.5.0
Version : Darwin Kernel Version 20.5.0: Sat May 8 05:10:33 PDT 2021; root:xnu-7195.121.3~9/RELEASE_X86_64
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 1.3.0
numpy : 1.21.0
pytz : 2020.1
dateutil : 2.8.1
pip : 21.1.3
setuptools : 56.0.0
Cython : 0.29.23
pytest : 6.2.4
hypothesis : None
sphinx : 4.0.2
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.6.3
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.2
IPython : 7.23.1
pandas_datareader: None
bs4 : 4.9.3
bottleneck : None
fsspec : 2021.06.0
fastparquet : 0.4.1
gcsfs : None
matplotlib : 3.4.2
numexpr : 2.7.2
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 4.0.1
pyxlsb : None
s3fs : 0.4.2
scipy : 1.7.0
sqlalchemy : 1.3.18
tables : 3.6.1
tabulate : 0.8.7
xarray : 0.18.2
xlrd : 1.2.0
xlwt : None
numba : 0.53.1