Fix duplicate bin detection for large cut inputs

[fallintoplace]

Summary

• Fix duplicate edge detection in cudf.cut.
• Add a regression test with 257 unique bin edges.

The old check used object identity when comparing the lengths of the input and its set of unique values. For larger edge lists, equal integer lengths can be different objects, so a sequence with unique edges could be reported as containing duplicates. The new check compares the values directly.

Testing

• python3 -m py_compile python/cudf/cudf/core/cut.py python/cudf/cudf/tests/general_functions/test_cut.py
• git diff --check

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[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 79764d7 and e471df2.

📒 Files selected for processing (1)

• python/cudf/cudf/tests/general_functions/test_cut.py

🚧 Files skipped from review as they are similar to previous changes (1)

• python/cudf/cudf/tests/general_functions/test_cut.py

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes

  • Improved duplicate bin-edge detection in cut, ensuring equal values are identified correctly even when represented by distinct objects.
  • Fixed binning with 256 unique bin edges when labels are disabled.

• Tests

  • Added regression coverage for 256 unique bin edges.
  • Added validation that duplicate large integer edges raise an error.

Walkthrough

The cut duplicate-bin-edge validation now uses value equality. Regression tests cover 256 unique bins and duplicate large integer edges represented by distinct objects.

Changes

Cut bin-edge validation

Layer / File(s)	Summary
Bin-edge validation and regression coverage python/cudf/cudf/core/cut.py, python/cudf/cudf/tests/general_functions/test_cut.py	The duplicate-bin-edge check now compares values instead of object identity. Tests compare 256 unique bins with pandas and verify that duplicate large integer edges raise ValueError.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Suggested reviewers: matt711

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the fix to duplicate bin detection in large cut inputs.
Description check	✅ Passed	The description explains the duplicate-edge detection fix and the regression test added for large bin-edge inputs.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@python/cudf/cudf/tests/general_functions/test_cut.py`:
- Around line 233-240: Extend test_cut_unique_bins_larger_than_integer_cache
with a duplicate-edge case using independently constructed equal integer objects
above 256, ensuring identity-based detection is exercised. Verify cut matches
pandas for the default duplicates="raise" behavior or explicitly test
duplicates="drop" with the corresponding expected result.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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📥 Commits

Reviewing files that changed from the base of the PR and between 6a22d1d and 06210a1.

📒 Files selected for processing (2)

• python/cudf/cudf/core/cut.py
• python/cudf/cudf/tests/general_functions/test_cut.py

[mroeschke]

Thanks. One question before I initiate the test suite

[mroeschke]

/ok to test e471df2