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https://issues.apache.org/jira/browse/ARROW-7617?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andrew Wieteska reassigned ARROW-7617:
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Assignee: (was: Andrew Wieteska)
> [Python] parquet.write_to_dataset creates empty partitions for non-observed
> dictionary items (categories)
> ---------------------------------------------------------------------------------------------------------
>
> Key: ARROW-7617
> URL: https://issues.apache.org/jira/browse/ARROW-7617
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.15.1
> Reporter: Vladimir
> Priority: Major
> Labels: dataset, dataset-parquet-write, parquet
> Fix For: 5.0.0
>
>
> Hello,
> it looks like, views with selection along categorical column are not properly
> respected.
> For the following dummy dataframe:
>
> {code:java}
> d = pd.date_range('1990-01-01', freq='D', periods=10000)
> vals = pd.np.random.randn(len(d), 4)
> x = pd.DataFrame(vals, index=d, columns=['A', 'B', 'C', 'D'])
> x['Year'] = x.index.year
> {code}
> The slice by Year is saved to partitioned parquet properly:
> {code:java}
> table = pa.Table.from_pandas(x[x.Year==1990], preserve_index=False)
> pq.write_to_dataset(table, root_path='test_a.parquet',
> partition_cols=['Year']){code}
> However, if we convert Year to pandas.Categorical - it will save the whole
> original dataframe, not only slice of Year=1990:
> {code:java}
> x['Year'] = x['Year'].astype('category')
> table = pa.Table.from_pandas(x[x.Year==1990], preserve_index=False)
> pq.write_to_dataset(table, root_path='test_b.parquet',
> partition_cols=['Year'])
> {code}
>
>
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