[jira] [Created] (ARROW-6302) [Python] parquet categorical support doesn't preserve order

["Galuh Sahid (Jira)" <ji...@apache.org>]

Galuh Sahid created ARROW-6302:
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             Summary: [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


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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