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GH-35830: [C++] Fix fixed-size list scalar hashing with non-zero offsets#48798

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HyukjinKwon wants to merge 1 commit intoapache:mainfrom
HyukjinKwon:GH-35830
Open

GH-35830: [C++] Fix fixed-size list scalar hashing with non-zero offsets#48798
HyukjinKwon wants to merge 1 commit intoapache:mainfrom
HyukjinKwon:GH-35830

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@HyukjinKwon HyukjinKwon commented Jan 9, 2026 •
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Rationale for this change

Fixed-size list scalars with equal values but different offsets were hashing to different values.

What changes are included in this PR?

  • Added FIXED_SIZE_LIST case in ArrayHash to scale child offsets by list_size
  • Added C++ test in scalar_test.cc for nested fixed-size lists
  • Added Python test in test_scalars.py

Are these changes tested?

Unit tests were added, and also manually tested.

Are there any user-facing changes?

Yes.

import pyarrow as pa

inner = pa.list_(pa.int32(), 2)
outer = pa.list_(inner, 3)
g = pa.array([[[1, 2], [3, 4], [5, 6]], [[7, 8], [9, 10], [11, 12]]], type=outer)
h = pa.array([[[7, 8], [9, 10], [11, 12]]], type=outer)
# Comparing `[[7, 8], [9, 10], [11, 12]]`
print(g[1] == h[0])
print(hash(g[1]) == hash(h[0]))

Before:

True
False

After:

True
True

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github-actions bot commented Jan 9, 2026

⚠️ GitHub issue #35830 has been automatically assigned in GitHub to PR creator.

@github-actions
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github-actions bot commented Jan 9, 2026

⚠️ GitHub issue #35830 has been automatically assigned in GitHub to PR creator.

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