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https://issues.apache.org/jira/browse/ARROW-3652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17660675#comment-17660675
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Rok Mihevc commented on ARROW-3652:
-----------------------------------
This issue has been migrated to [issue
#19959|https://github.com/apache/arrow/issues/19959] on GitHub. Please see the
[migration documentation|https://github.com/apache/arrow/issues/14542] for
further details.
> [Python] CategoricalIndex is lost after reading back
> ----------------------------------------------------
>
> Key: ARROW-3652
> URL: https://issues.apache.org/jira/browse/ARROW-3652
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.11.1
> Reporter: Armin Berres
> Assignee: Wes McKinney
> Priority: Major
> Labels: parquet, pull-request-available
> Fix For: 0.15.0
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> When a {{CategoricalIndex}} is written and read back the resulting index is
> not more categorical.
> {code}
> df = pd.DataFrame([['a', 'b'], ['c', 'd']], columns=['c1', 'c2'])
> df['c1'] = df['c1'].astype('category')
> df = df.set_index(['c1'])
> table = pa.Table.from_pandas(df)
> pq.write_table(table, 'test.parquet')
> ref_df = pq.read_pandas('test.parquet').to_pandas()
> print(df.index)
> # CategoricalIndex(['a', 'c'], categories=['a', 'c'], ordered=False,
> name='c1', dtype='category')
> print(ref_df.index)
> # Index(['a', 'c'], dtype='object', name='c1')
> {code}
> In the metadata the information is correctly contained:
> {code:java}
> {"name": "c1", "field_name": "c1", "p'
> b'andas_type": "categorical", "numpy_type": "int8", "metadata":
> {"'
> b'num_categories": 2, "ordered": false}
> {code}
>
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