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https://issues.apache.org/jira/browse/ARROW-6302?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16911760#comment-16911760
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Wes McKinney commented on ARROW-6302:
-------------------------------------
Yeah this should be easy to fix. The changes need to be based on top of
https://github.com/apache/arrow/pull/5138 (or wait for it to be merged) to
avoid rebase conflicts
> [Python] parquet categorical support doesn't preserve order
> -----------------------------------------------------------
>
> Key: ARROW-6302
> URL: https://issues.apache.org/jira/browse/ARROW-6302
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.15.0
> Reporter: Galuh Sahid
> Priority: Major
> Labels: parquet
>
> In pandas, I tried roundtripping to parquet with {{to_parquet}} and
> {{read_parquet}}. It preserves categorical dtypes but does not preserve their
> order.
> {code:python}
> import pandas as pd
> from pandas.io.parquet import read_parquet, to_parquet
> df = pd.DataFrame()
> df["a"] = pd.Categorical(["a", "b", "c", "a"], categories=["b", "c", "d"],
> ordered=True)
> df.to_parquet(<path>)
> actual = read_parquet(<path>)
> df["a"]
> 0 NaN
> 1 b
> 2 c
> 3 NaN
> Name: a, dtype: category
> Categories (3, object): [b < c < d]
> actual["a"]
> 0 NaN
> 1 b
> 2 c
> 3 NaN
> Name: a, dtype: category
> Categories (3, object): [b, c, d]
> {code}
>
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