[jira] [Commented] (ARROW-1644) [C++][Parquet] Read and write nested Parquet data with a mix of struct and list nesting levels

[Wes McKinney (JIRA)]

    [ 
https://issues.apache.org/jira/browse/ARROW-1644?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16877937#comment-16877937
 ] 

Wes McKinney commented on ARROW-1644:
-------------------------------------

Yes, essentially. 

1-level encoding

{code}
group schema {
  optional INT32 some_other_value
  repeated T list_item;
}
{code}

2-level encoding

{code}
group schema {
  optional INT32 some_other_value
  repeated group list_value {
    optional/required T list_item;
  }
}
{code}

3-level encoding

{code}
group schema {
  optional INT32 some_other_value
  optional/required group list_value LIST {
    repeated group box {
      optional/required T list_item;
    }
  }
}
{code}

note

* The 1-level encoding can only encode {{array<item NOT NULL> NOT NULL}}. 
* The 2-level encoding can only encode {{array<item> NOT NULL}}
* The 3-level encoding can encode either nullity of list items or the lists 
themselves {{array<item [nullable?]> [nullable?]}}

The decode path is slightly different for the 1/2 level cases

> [C++][Parquet] Read and write nested Parquet data with a mix of struct and 
> list nesting levels
> ----------------------------------------------------------------------------------------------
>
>                 Key: ARROW-1644
>                 URL: https://issues.apache.org/jira/browse/ARROW-1644
>             Project: Apache Arrow
>          Issue Type: New Feature
>          Components: C++, Python
>    Affects Versions: 0.8.0
>            Reporter: DB Tsai
>            Assignee: Micah Kornfield
>            Priority: Major
>              Labels: parquet, pull-request-available
>             Fix For: 1.0.0
>
>
> We have many nested parquet files generated from Apache Spark for ranking 
> problems, and we would like to load them in python for other programs to 
> consume. 
> The schema looks like 
> {code:java}
> root
>  |-- profile_id: long (nullable = true)
>  |-- country_iso_code: string (nullable = true)
>  |-- items: array (nullable = false)
>  |    |-- element: struct (containsNull = false)
>  |    |    |-- show_title_id: integer (nullable = true)
>  |    |    |-- duration: double (nullable = true)
> {code}
> And when I tried to load it with nightly build pyarrow on Oct 4, 2017, I got 
> the following error.
> {code:python}
> Python 3.6.2 |Anaconda, Inc.| (default, Sep 30 2017, 18:42:57) 
> [GCC 7.2.0] on linux
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import numpy as np
> >>> import pandas as pd
> >>> import pyarrow as pa
> >>> import pyarrow.parquet as pq
> >>> table2 = pq.read_table('part-00000')
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "/home/dbt/miniconda3/lib/python3.6/site-packages/pyarrow/parquet.py", 
> line 823, in read_table
>     use_pandas_metadata=use_pandas_metadata)
>   File "/home/dbt/miniconda3/lib/python3.6/site-packages/pyarrow/parquet.py", 
> line 119, in read
>     nthreads=nthreads)
>   File "_parquet.pyx", line 466, in pyarrow._parquet.ParquetReader.read_all
>   File "error.pxi", line 85, in pyarrow.lib.check_status
> pyarrow.lib.ArrowNotImplementedError: lists with structs are not supported.
> {code}
> I somehow get the impression that after 
> https://issues.apache.org/jira/browse/PARQUET-911 is merged, we should be 
> able to load the nested parquet in pyarrow. 
> Any insight about this? 
> Thanks.



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