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

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

  • [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

Note: Please read this guide detailing how to provide the necessary information for us to reproduce your bug.

Code Sample, a copy-pastable example

import pandas as pd

df = pd.DataFrame([0,1,2]).append(pd.DataFrame([3,4,5]))
df.columns = ['a']
print(df - df.a)

Problem description

Why we can not to do binary operations when we work with DataFrame and Series(dataframe has 1 columns, len(df.index)==len(series.index)) with duplicated indexes? If left and right operands have the same type (DataFrame/DataFrame` for example) it works.

Expected Output

0    0
1    0
2    0
0    0
1    0
2    0

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit : 67a3d4241ab84419856b84fc3ebc9abcbe66c6b3 python : 3.8.3.final.0 python-bits : 64 OS : Linux OS-release : 4.15.0-50-generic Version : #54-Ubuntu SMP Mon May 6 18:46:08 UTC 2019 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : en_US LOCALE : en_US.ISO8859-1 pandas : 1.1.4 numpy : 1.19.2 pytz : 2020.1 dateutil : 2.8.1 pip : 20.0.2 setuptools : 46.4.0.post20200518 Cython : None pytest : 6.1.1 hypothesis : None sphinx : None blosc : None feather : 0.4.1 xlsxwriter : None lxml.etree : 4.5.2 html5lib : None pymysql : None psycopg2 : None jinja2 : 2.11.2 IPython : None pandas_datareader: None bs4 : 4.9.3 bottleneck : None fsspec : 0.8.3 fastparquet : None gcsfs : None matplotlib : 3.2.2 numexpr : 2.7.1 odfpy : None openpyxl : 3.0.5 pandas_gbq : 0.14.0 pyarrow : 1.0.0 pytables : None pyxlsb : None s3fs : 0.5.1 scipy : 1.5.2 sqlalchemy : 1.3.19 tables : 3.6.1 tabulate : None xarray : 0.16.1 xlrd : 1.2.0 xlwt : None numba : None

Comment From: phofl

Hi, thanks for your report. When executing this on master, I get the expected output. Seems to be fixed

Comment From: rhshadrach

@phofl: On master I get:

ValueError: cannot reindex from a duplicate axis

Comment From: phofl

Hm, seems that I was on a feature branch locally, which did not raise the error. I will try to find out which one...

Comment From: phofl

Hm weird, can not replicate this...

Comment From: rhshadrach

@phofl: By "this" do you mean you can't replicate the ValueError or can't replicate the feature branch fix?

Comment From: phofl

Unfortunately I can not replicate the fix :( Tested all branches...

Comment From: jbrockmendel

This works correctly on main, but the user is incorrectly expecting this to behave like df.sub(df.a, axis=0) instead of df.sub(df.a, axis=1).