[jira] [Assigned] (ARROW-10134) [C++][Dataset] Add ParquetFileFragment::num_row_groups property

["Ben Kietzman (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-10134?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ben Kietzman reassigned ARROW-10134:
------------------------------------

    Assignee: Ben Kietzman

> [C++][Dataset] Add ParquetFileFragment::num_row_groups property
> ---------------------------------------------------------------
>
>                 Key: ARROW-10134
>                 URL: https://issues.apache.org/jira/browse/ARROW-10134
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Joris Van den Bossche
>            Assignee: Ben Kietzman
>            Priority: Major
>              Labels: dataset, dataset-dask-integration
>             Fix For: 2.0.0
>
>
> From https://github.com/dask/dask/pull/6534#issuecomment-699512602, comment by [~rjzamora]:
> bq.  it would be great to have access the total row-group count for the fragment from a {{num_row_groups}} attribute (which pyarrow should be able to get without parsing all row-group metadata/statistics - I think?).
> One question is: does this attribute correspond to the row groups in the parquet file, or the (subset of) row groups represented by the fragment? 
> I expect the second (so if you do SplitByRowGroup, you would get a fragment with num_row_groups==1), but this might be a potential confusing aspect of the attribute.



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