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BUG: Index.difference is returning too many values #58971

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michaelpradel opened this issue Jun 10, 2024 · 2 comments · May be fixed by #59148
Open
3 tasks done

BUG: Index.difference is returning too many values #58971

michaelpradel opened this issue Jun 10, 2024 · 2 comments · May be fixed by #59148
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@TiffL
Labels
Bug Index Related to the Index class or subclasses Regression Functionality that used to work in a prior pandas version setops union, intersection, difference, symmetric_difference
Milestone
2.2.3

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@michaelpradel
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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

index1 = pd.period_range('2022-01-01', periods=5, freq='M')
index2 = pd.Index(['2022-02', '2022-03'])
result = index1.difference(index2)
print(result)

Issue Description

The example creates index1 with 5 months, and index2 with two months. The difference should be an index with three months. However, I'm getting the following:

PeriodIndex(['2022-01', '2022-02', '2022-03', '2022-04', '2022-05'], dtype='period[M]')

Looks like this issue was introduced by #55108.

Expected Behavior

The example should print the following:

Index(['2022-02', '2022-03'], dtype='object')

Pandas 2.1.4 gives the expected behavior.

Installed Versions

INSTALLED VERSIONS ------------------ commit : 6dbeeb4 python : 3.10.8.final.0 python-bits : 64 OS : Linux OS-release : 6.5.0-35-generic Version : #35-Ubuntu SMP PREEMPT_DYNAMIC Fri Apr 26 11:23:57 UTC 2024 machine : x86_64 processor : byteorder : little LC_ALL : None LANG : C.UTF-8 LOCALE : en_US.UTF-8

pandas : 2.2.0rc0+28.g6dbeeb4009
numpy : 1.26.4
pytz : 2024.1
dateutil : 2.9.0.post0
setuptools : 63.2.0
pip : 24.0
Cython : 3.0.10
pytest : 8.2.0
hypothesis : 6.100.2
sphinx : 7.3.7
blosc : None
feather : None
xlsxwriter : 3.2.0
lxml.etree : 5.2.1
html5lib : 1.1
pymysql : 1.4.6
psycopg2 : 2.9.9
jinja2 : 3.1.3
IPython : 8.24.0
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
bottleneck : 1.3.8
fastparquet : 2024.2.0
fsspec : 2024.3.1
gcsfs : 2024.3.1
matplotlib : 3.8.4
numba : 0.59.1
numexpr : 2.10.0
odfpy : None
openpyxl : 3.1.2
pyarrow : 16.0.0
pyreadstat : 1.2.7
python-calamine : None
pyxlsb : 1.0.10
s3fs : 2024.3.1
scipy : 1.13.0
sqlalchemy : 2.0.29
tables : 3.9.2
tabulate : 0.9.0
xarray : 2024.3.0
xlrd : 2.0.1
zstandard : 0.22.0
tzdata : 2024.1
qtpy : None
pyqt5 : None
@michaelpradel michaelpradel added Bug Needs Triage Issue that has not been reviewed by a pandas team member labels Jun 10, 2024
@Aloqeely
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Thanks for the report! On 2.2, index1.difference(index2) does produce incorrect results but index2.difference(index1) works correctly, on 2.1.4 and before it is the opposite (i.e. index2.difference(index1) produces wrong result)

PRs are welcome to fix this, ideally fixing both cases here.

@Aloqeely Aloqeely added Regression Functionality that used to work in a prior pandas version Index Related to the Index class or subclasses setops union, intersection, difference, symmetric_difference and removed Needs Triage Issue that has not been reviewed by a pandas team member labels Jun 13, 2024
@Aloqeely Aloqeely added this to the 2.2.3 milestone Jun 13, 2024
@TiffL
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TiffL commented Jun 25, 2024 •
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Taking a look, looks like may be due to the difference in dtype

@TiffL TiffL linked a pull request Jun 29, 2024 that will close this issue
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@TiffL TiffL

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Bug Index Related to the Index class or subclasses Regression Functionality that used to work in a prior pandas version setops union, intersection, difference, symmetric_difference
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Milestone
2.2.3
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BUG: Fix difference functionality for Period Indexes TiffL/pandas
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@michaelpradel @TiffL @Aloqeely