[jira] [Commented] (ARROW-2450) [Python] Saving to parquet fails for empty lists

["Antoine Pitrou (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-2450?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16435479#comment-16435479 ] 

Antoine Pitrou commented on ARROW-2450:
---------------------------------------

Apparently Parquet produces a null array instead of a list array for that column.

> [Python] Saving to parquet fails for empty lists
> ------------------------------------------------
>
>                 Key: ARROW-2450
>                 URL: https://issues.apache.org/jira/browse/ARROW-2450
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>    Affects Versions: 0.9.0
>            Reporter: Uwe L. Korn
>            Priority: Major
>             Fix For: 0.9.1
>
>
> When writing a table to parquet through pandas, if any column includes an empty list, it fails with a segmentation fault.
> Minimal example:
> {code}
> import pyarrow as pa
> import pyarrow.parquet as pq
> import pandas as pd
> def save(rows):
>     table1 = pa.Table.from_pandas(pd.DataFrame(rows))
>     pq.write_table(table1, 'test-foo.pq')
>     table2 = pq.read_table('test-foo.pq')
>     print('ROWS:', rows)
>     print('TABLE1:', table1.to_pandas(), sep='\n')
>     print('TABLE2:', table2.to_pandas(), sep='\n')
> save([{'val': ['something']}])
> print('---')
> save([{'val': []}])  # empty
> {code}
> Output:
> {code}
> ROWS: [{'val': ['something']}]
> TABLE1:
>            val
> 0  [something]
> TABLE2:
>            val
> 0  [something]
> ---
> ROWS: [{'val': []}]
> TABLE1:
>   val
> 0  []
> [1]    13472 segmentation fault (core dumped)  python3 test.py
> {code}
> Versions:
> {code}
> $ pip3 list | grep pyarrow
> pyarrow (0.9.0)
> $ python3 --version
> Python 3.5.2
> {code}



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