BUG: join: ValueError: Indexes have overlapping values

[anmyachev]

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Reproducible Example

import pandas as pd

test = pandas.DataFrame({"col1": [1,2]})
test.join(test, lsuffix="b")  # OK
test.join([test], lsuffix="b")  # failed
# *** ValueError: Indexes have overlapping values: Index(['col1'], dtype='object')

Issue Description

Unexpected behavior.

Expected Behavior

The result of calling join function in the cases above should lead to the same result.

Installed Versions

INSTALLED VERSIONS

commit : 06d2301
python : 3.8.12.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19044
machine : AMD64
processor : Intel64 Family 6 Model 142 Stepping 12, GenuineIntel
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : English_United States.1252

pandas : 1.4.1
numpy : 1.22.2
pytz : 2021.3
dateutil : 2.8.2
pip : 22.0.3
setuptools : 59.8.0
Cython : None
pytest : 7.0.0
hypothesis : None
sphinx : 4.4.0
blosc : None
feather : 0.4.1
xlsxwriter : None
lxml.etree : 4.7.1
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 8.0.1
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : None
fsspec : 2022.01.0
gcsfs : None
matplotlib : 3.2.2
numba : None
numexpr : 2.7.3
odfpy : None
openpyxl : 3.0.9
pandas_gbq : 0.17.0
pyarrow : 6.0.1
pyreadstat : None
pyxlsb : None
s3fs : 2022.01.0
scipy : 1.8.0
sqlalchemy : 1.4.31
tables : 3.7.0
tabulate : None
xarray : 0.21.1
xlrd : 2.0.1
xlwt : None
zstandard : None

[sappersapper]

It seems the merge() in 'else:' branch does not take into account the 'suffixes' parameters.

pandas/pandas/core/frame.py

Lines 9466 to 9468 in 6033ed4

	joined = merge(
	joined, frame, how=how, left_index=True, right_index=True
	)

Just add a conversion of the input 'other' at the beginning of _join_compat() ?

if isinstance(other, list) and len(other) == 1:
    other = other[0]

or add 'suffixes' parameters to merge() in 'else:' branch ?

How to deal with test.join([test, test], lsuffix="b") ?

[bwozniak27]

take

[bwozniak27]

Should this operation be allowed? In the comment for Join():

Notes
-----
Parameters on, lsuffix, and rsuffix are not supported when
passing a list of DataFrame objects.

Since the suffixes are added for the sake of differentiating the columns when merged, how would that work with an DataFrame array of size > 1? In this case, there would still be columns of the same name. I see two reasonable solutions.

1. We allow them to do this, and for each when adding the suffix, attach a counter onto it (ex. "1" or "_1")

test.join([test, test], lsuffix="b")

   col1b_1  col1b_2  col1b_3  col1
0       1       3            5    7
1       2       4            6    8

2. We make a more explicit error when a user attempts to use either of the suffix parameters. Currently there is not check for them, only a check for the on parameter.

I am a student in college and am new to open source contributing, so I was wondering if I could get some assistance. Thanks so much.
@anmyachev @sappersapper

[anmyachev]

Hello @bwozniak27! I'm glad you are interested in this issue.

I like the second option. For example, I didn’t read these lines in the documentation :)
As for the first option, I'm not sure, but in the case of a list of one element, it would be possible to make the behavior similar to the case when a simple dataframe is passed (as @sappersapper suggested).