[jira] [Created] (ARROW-11497) [Python] pyarrow parquet writer for list does not conform with Apache Parquet sepecification

["Truc Lam Nguyen (Jira)" <ji...@apache.org>]

Truc Lam Nguyen created ARROW-11497:
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             Summary: [Python] pyarrow parquet writer for list does not conform with Apache Parquet sepecification
                 Key: ARROW-11497
                 URL: https://issues.apache.org/jira/browse/ARROW-11497
             Project: Apache Arrow
          Issue Type: Bug
          Components: Python
    Affects Versions: 3.0.0
            Reporter: Truc Lam Nguyen
         Attachments: parquet-tools-meta.log

Sorry if I don't know this feature is done deliberately, but it looks like the parquet writer for list data type does not confirm to Apache Parquet list logical type specification,

According to this page: [https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#lists,] list type contains 3 level where the middle level, named {{list}}, must be a repeated group with a single field named _{{element}}_

However, in the parquet file from pyarrow writer, that single field is named _item_ instead,

Please find below the example python code that produce a parquet file (I use pandas version 1.2.1 and pyarrow version 3.0.0)

 
{code:java}
import pandas as pd
 
df = pd.DataFrame(data=[ {'studio': 'blizzard', 'games': [{'name': 'diablo', 'version': '3'}, {'name': 'star craft', 'version': '2'}]}, {'studio': 'ea', 'games': [{'name': 'fifa', 'version': '21'}]}, ])
df.to_parquet('/tmp/test.parquet', engine='pyarrow')
{code}
 

Then I use parquet-tools from [https://formulae.brew.sh/formula/parquet-tools] to check the metadata of parquet file via this command

parquet-tools meta /tmp/test.parquet

The full meta is included in attached, here is only an extraction of list type column

games: OPTIONAL F:1 
.list: REPEATED F:1 
..item: OPTIONAL F:2 
...name: OPTIONAL BINARY L:STRING R:1 D:4
...version: OPTIONAL BINARY L:STRING R:1 D:4

as can be seen, under list, it is single field named _item_

I think this should be made to be name _element_ to conform with Apache Parquet specification.



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