Repository navigation
Preserve null maps when projecting a map of structs - #4118
Merged
Merged
Conversation
Fokko
reviewed
Oct 18, 2026
Fokko
left a comment
Fokko
left a comment
Contributor
There was a problem hiding this comment.
Great catch @syahra712 Thanks for adding the test as well 👍 I have one suggestion
Fokko
approved these changes
Oct 18, 2026
Fokko
left a comment
Fokko
left a comment
Contributor
There was a problem hiding this comment.
Looks good, thanks @syahra712 🙌
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Rationale for this change
Closes #4114.
When
ArrowProjectionVisitor.map()rebuilds a map whose values are structs, it callspa.MapArray.from_arrays(offsets, keys, values). That drops the validity bitmap of the original array, so null maps come back as empty maps ({}) after projection. This is the map counterpart of the list issue handled in #4065.The fix keeps the validity and offsets buffers of the original map array and only swaps in the projected child array, so nulls (and slicing offsets) are preserved.
Are these changes tested?
Yes. Added
test__to_requested_schema_null_map_of_structsintests/io/test_pyarrow.py, covering a map with struct values, a map with primitive values, and a sliced batch. The test fails onmain(null rows become[]) and passes with the fix.Are there any user-facing changes?
Null map columns with struct values are now read back as null instead of an empty map.