fix: Preserve numRows for zero-column RecordBatch in IPC#402
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rustyconover wants to merge 1 commit intoapache:mainfrom
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fix: Preserve numRows for zero-column RecordBatch in IPC#402rustyconover wants to merge 1 commit intoapache:mainfrom
rustyconover wants to merge 1 commit intoapache:mainfrom
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When a zero-column RecordBatch is deserialized from IPC, ensureSameLengthData in the RecordBatch constructor recomputes length from children via chunks.reduce((max, col) => Math.max(max, col.length), 0). With zero children, this always returns 0 — discarding the original length from the IPC message header. Pass this.data.length to ensureSameLengthData as the explicit maxLength parameter, which the function already accepts as an optional third argument. For batches with columns, this.data.length already matches the max column length, so there is no behavior change. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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kou
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Mar 5, 2026
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Can we create this file by our writer in test instead of adding this file to the repository?
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Pull request overview
Fixes Arrow JS RecordBatch construction so that zero-column batches preserve numRows when deserialized from IPC, matching other Arrow implementations and the IPC message header.
Changes:
- Pass
this.data.lengthas the explicitmaxLengthtoensureSameLengthData()in the[Schema, Data]RecordBatchconstructor path. - Add unit tests covering PyArrow interop, JS IPC round-trip, and direct constructor behavior for zero-column batches.
- Add a PyArrow-generated IPC stream fixture containing a zero-column
RecordBatchwith 100 rows.
Reviewed changes
Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
src/recordbatch.ts |
Preserves parent Data.length when normalizing children, fixing zero-column length loss. |
test/unit/ipc/reader/zero-column-batch-tests.ts |
Adds regression tests to ensure numRows stays correct across read/write and direct construction. |
test/data/zero_column_batch.arrow |
Adds a PyArrow-generated IPC fixture for interop/regression testing. |
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Summary
When a zero-column RecordBatch is deserialized from IPC,
ensureSameLengthDatain the
RecordBatchconstructor recomputes length from children viachunks.reduce((max, col) => Math.max(max, col.length), 0). With zero children,this always returns 0 — discarding the original length from the IPC message header.
Other Arrow implementations (PyArrow, Arrow Go, arrow-rs) correctly preserve
numRows for zero-column batches.
Fix
Pass
this.data.lengthtoensureSameLengthDataas the explicitmaxLengthparameter, which the function already accepts as an optional third argument.
For batches with columns,
this.data.lengthalready matches the max columnlength, so there is no behavior change.
Tests
Closes #401