Ged Steponavicius created ARROW-8251:
----------------------------------------
Summary: [Python] pandas.ExtensionDtype does not survive round
trip with write_to_dataset
Key: ARROW-8251
URL: https://issues.apache.org/jira/browse/ARROW-8251
Project: Apache Arrow
Issue Type: Bug
Components: Python
Affects Versions: 0.16.0
Environment: pandas 1.0.1
parquet 0.16
Reporter: Ged Steponavicius
write_to_dataset with pandas fields using pandas.ExtensionDtype nullable int or
string produce parquet file which when read back in has different dtypes than
original df
{code:java}
import pandas as pd
import pyarrow as pa
import pyarrow.parquet as pq
parquet_dataset = 'partquet_dataset/'
parquet_file = 'test.parquet'
df = pd.DataFrame([{'str_col':'abc','int_col':1,'part':1},
{'str_col':np.nan,'int_col':np.nan,'part':1}])
df['str_col'] = df['str_col'].astype(pd.StringDtype())
df['int_col'] = df['int_col'].astype(pd.Int64Dtype())
table = pa.Table.from_pandas(df)
pq.write_to_dataset(table, root_path=parquet_dataset, partition_cols=['part'] )
pq.write_table(table, where=parquet_file) {code}
write_table handles schema correctly, pandas.ExtensionDtype survive round trip:
{code:java}
pq.read_table(parquet_file).to_pandas().dtypes
str_col string
int_col Int64
part int64 {code}
However, write_to_dataset reverts back to object/float:
{code:java}
pq.read_table(parquet_dataset).to_pandas().dtypes
str_col object
int_col float64
part category {code}
I have also tried writing common metadata at the top-level directory of a
partitioned dataset and then passing metadata to read_table, but results are
the same as without metadata
{code:java}
pq.write_metadata(table.schema, parquet_dataset+'_common_metadata',
version='2.0') meta = pq.read_metadata(parquet_dataset+'_common_metadata')
pq.read_table(parquet_dataset,metadata=meta).to_pandas().dtypes {code}
This also affects pandas to_parquet when partition_cols is specified:
{code:java}
df.to_parquet(path = parquet_dataset, partition_cols=['part'])
pd.read_parquet(parquet_dataset).dtypes
str_col object
int_col float64
part category {code}
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
