[Python] Selective projection of struct fields errors with use_legacy_dataset = False #29424
Description
Selectively projecting fields from within a struct when reading from parquet files triggers an ArrowInvalid error when using the new dataset api (use_legacy_dataset=False). Passing use_legacy_dataset=True yields the expected behavior: loading only the columns enumerated in the columns argument, recursing into structs if there is a . delimeter in the field name.
Using the following test table:
df = pd.DataFrame({
'user_id': ['abc123', 'qrs456'],
'interaction': [{'type': 'click', 'element': 'button'}, {'type':'scroll', 'element': 'window'}]
})
table = pa.Table.from_pandas(df)
pq.write_table(table, 'example.parquet')Using the current default datasets API:
table_latest = pq.read_table('example.parquet', columns = ['user_id', 'interaction.type'])yields:
---------------------------------------------------------------------------
ArrowInvalid Traceback (most recent call last)
<ipython-input-25-982ca2d96075> in <module>
----> 1 table_latest = pq.read_table('/'.join([out_path, 'example.parquet']), columns = ['user_id', 'interaction.type'], filesystem = fs)
2 table_latest
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/parquet.py in read_table(source, columns, use_threads, metadata, use_pandas_metadata, memory_map, read_dictionary, filesystem, filters, buffer_size, partitioning, use_legacy_dataset, ignore_prefixes, pre_buffer, coerce_int96_timestamp_unit)
1894
1895 return dataset.read(columns=columns, use_threads=use_threads,
-> 1896 use_pandas_metadata=use_pandas_metadata)
1897
1898 if ignore_prefixes is not None:
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/parquet.py in read(self, columns, use_threads, use_pandas_metadata)
1744 table = self._dataset.to_table(
1745 columns=columns, filter=self._filter_expression,
-> 1746 use_threads=use_threads
1747 )
1748
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/_dataset.pyx in pyarrow._dataset.Dataset.to_table()
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/_dataset.pyx in pyarrow._dataset.Dataset.scanner()
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/_dataset.pyx in pyarrow._dataset.Scanner.from_dataset()
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/_dataset.pyx in pyarrow._dataset._populate_builder()
/usr/local/share/sciencebox/venv/lib/python3.6/site-packages/pyarrow/error.pxi in pyarrow.lib.check_status()
ArrowInvalid: No match for FieldRef.Name(interaction.type) in user_id: string
interaction: struct<element: string, type: string>
Whereas:
table_legacy = pq.read_table('example.parquet', columns = ['user_id', 'interaction.type'], use_legacy_dataset = True)Yields:
pyarrow.Table
user_id: string
interaction: struct<type: string>
child 0, type: string
Environment: Python 3.6.9
Reporter: Mark Grey
Related issues:
- [Python] Allow to create field reference to nested field (is blocked by)
Note: This issue was originally created as ARROW-13798. Please see the migration documentation for further details.