[C++] Slice RecordBatch of String array with offset 0 returns whole batch

[asfimport]

We are seeing a very similar bug as in ARROW-809, just for a RecordBatch of strings. A slice of a RecordBatch with a string column and offset =0 returns the whole batch instead.

 

import pandas as pd
import pyarrow as pa
df = pd.DataFrame({ 'b': ['test' for x in range(1000_000)]})
tbl = pa.Table.from_pandas(df)
batch = tbl.to_batches()[0]

batch.slice(0,2).serialize().size
# 4000232

batch.slice(1,2).serialize().size
# 240

 

Reporter: Sascha Hofmann / @saschahofmann
Assignee: Wes McKinney / @wesm

PRs and other links:

• GitHub Pull Request #5126

_{Note: This issue was originally created as ARROW-6046. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
The offsets buffer is not truncated in the first case. The logic for this is found here

https://github.com/apache/arrow/blob/master/cpp/src/arrow/ipc/writer.cc#L226

A correct fix would be to slice the offsets buffer to the expected length (plus padding, if it exists) when the offset is zero rather than serializing the whole thing

[asfimport]

Francois Saint-Jacques / @fsaintjacques:
Issue resolved by pull request 5126
#5126