[ARROW-8729] [C++][Dataset] Only selecting a partition column results in empty table

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.0.0
• Component/s: C++
• Labels: dataset dataset-dask-integration pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/24882
• Assignee: Ben Kietzman
• Reporter: Joris Van den Bossche
• Created: 07/May/20 10:02
• Updated: 11/Jan/23 08:02
• Resolved: 14/Jul/20 16:24

Description

Python reproducer:

import pyarrow as pa
import pyarrow.parquet as pq
import pyarrow.dataset as ds
path = "test_dataset"

table = pa.table({'part': ['a', 'a', 'b', 'b'], 'col': [1, 2, 3, 4]})
pq.write_to_dataset(table, str(path), partition_cols=["part"])

gives

In [38]: ds.dataset(str(path), partitioning="hive").to_table().num_rows                                                                                                                                            
Out[38]: 4

In [39]: ds.dataset(str(path), partitioning="hive").to_table(columns=["part"]).num_rows                                                                                                                            
Out[39]: 0

The schema correctly only includes the "part" column, but there are no rows.

cc bkietz

Issue Links

• links to: GitHub Pull Request #7534