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[BUG] Index.difference does not uniquify output for duplicate indexes #14489

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wence- opened this issue Nov 23, 2023 · 2 comments · Fixed by #14789
Closed

[BUG] Index.difference does not uniquify output for duplicate indexes #14489

wence- opened this issue Nov 23, 2023 · 2 comments · Fixed by #14789
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bug Something isn't working good first issue Good for newcomers Python Affects Python cuDF API.
Milestone
Pandas API Alignm...

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@wence-
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wence- commented Nov 23, 2023 •
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Describe the bug

cudf computes Index.difference with a leftanti join. This preserves duplicates in the left index. In contrast, pandas always produces an index with uniquified values.

Steps/Code to reproduce bug

import cudf
import pandas as pd

left = pd.Index([1, 1, 2, 2])
right = pd.Index([2])

print(left.difference(right))
cleft = cudf.from_pandas(left)
cright = cudf.from_pandas(cright)
print(cleft.difference(cright))

Expected behavior

Match pandas, either by calling drop_duplicates or using libcudf.search.contains (see also #14487).

Notes

Doesn't apply to MultiIndex right now, because that goes through pandas (although that's a perf bug that should be fixed).
@wence- wence- added bug Something isn't working Needs Triage Need team to review and classify pandas Python Affects Python cuDF API. and removed Needs Triage Need team to review and classify labels Nov 23, 2023
@wence- wence- added the good first issue Good for newcomers label Nov 24, 2023
@amiralimi
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Hi @wence- . Can I fix this issue?

@wence-
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wence- commented Jan 8, 2024

Hi @wence- . Can I fix this issue?

Please go ahead! When you open a PR please tag me so I don't miss it, thanks!

@amiralimi amiralimi mentioned this issue Jan 19, 2024
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rapids-bot bot pushed a commit that referenced this issue Jan 25, 2024
@amiralimi
Fix index difference to follow the pandas format (#14789)
0cd58fb 
This PR fixes an error in `Index.difference` where the function keeps duplicate elements while pandas removes the duplicates. The tests had no inputs with duplicates, so I added new tests too (I added the test from the original issue). 

- closes #14489

Authors:
  - AmirAli Mirian (https://github.com/amiralimi)
  - Ashwin Srinath (https://github.com/shwina)

Approvers:
  - Lawrence Mitchell (https://github.com/wence-)

URL: #14789
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bug Something isn't working good first issue Good for newcomers Python Affects Python cuDF API.
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Pandas API Alignment and Coverage
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Fix index difference to follow the pandas format amiralimi/cudf
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@wence- @amiralimi