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https://issues.apache.org/jira/browse/ARROW-10134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17209505#comment-17209505
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Joris Van den Bossche commented on ARROW-10134:
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For checking if it is a subselection of row groups, we could also have
something like a {{IsSubset}} method? That's maybe simpler as a
{{whole_file_fragment}} and covers an important example use case you gave for
{{whole_file_fragment}}
> [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, pull-request-available
> Fix For: 2.0.0
>
> Time Spent: 1.5h
> Remaining Estimate: 0h
>
> 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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