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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