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Stefan WangandAlenka Frim
f52076ca06
### Rationale for this change
Round-tripping an empty table through `to_struct_array()` and
`Table.from_struct_array()` raises
`ValueError: Must pass schema, or at least one RecordBatch`.
`to_struct_array()` returns a zero-chunk struct `ChunkedArray`, so
`from_struct_array()` has no batch from which to recover the schema.
For a zero-chunk input, `from_struct_array()` now calls `combine_chunks()` and
converts the resulting empty struct array into a `RecordBatch`. Nonempty inputs
keep the existing path. An empty non-struct `ChunkedArray` still raises the
expected `TypeError`.
### What changes are included in this PR?
The empty `ChunkedArray` path creates one empty batch before calling
`Table.from_batches`. The regression coverage checks the round-trip result,
schema preservation, and the invalid non-struct input.
### Are these changes tested?
I ran this script against PyArrow 25.0.1 and the compiled branch:
```bash
python - <<'PY'
import pyarrow as pa
value = pa.chunked_array(
[], type=pa.struct([("ints", pa.int32()), ("floats", pa.float32())])
)
print(f"pyarrow={pa.__version__}, chunks={value.num_chunks}")
try:
result = pa.Table.from_struct_array(value)
print(f"rows={result.num_rows}, schema={result.schema}")
except Exception as error:
print(f"{type(error).__name__}: {error}")
PY
```
Before:
```text
pyarrow=25.0.1, chunks=0
ValueError: Must pass schema, or at least one RecordBatch
```
After:
```text
pyarrow=26.0.0.dev175+ge4ad179ae, chunks=0
rows=0, schema=ints: int32
floats: float
```
The focused regression suite also runs against the compiled branch:
```text
$ python -m pytest python/pyarrow/tests/test_table.py -k from_struct_array -q
....... [100%]
7 passed, 208 deselected in 0.51s
```
### Are there any user-facing changes?
`Table.from_struct_array()` now returns the expected empty table for a
zero-chunk struct `ChunkedArray` instead of raising `ValueError`.
* GitHub Issue: https://github.com/apache/arrow/issues/48344
* GitHub Issue: #48344
Lead-authored-by: 1fanwang <1fannnw@gmail.com>
Co-authored-by: Alenka Frim <AlenkaF@users.noreply.github.com>
Signed-off-by: AlenkaF <frim.alenka@gmail.com>