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Posted to jira@arrow.apache.org by "Joris Van den Bossche (Jira)" <ji...@apache.org> on 2020/06/16 15:17:00 UTC
[jira] [Updated] (ARROW-9147) [C++][Dataset] Support null -> other
type promotion in Dataset scanning
[ https://issues.apache.org/jira/browse/ARROW-9147?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Joris Van den Bossche updated ARROW-9147:
-----------------------------------------
Labels: dataset dataset-dask-integration (was: dataset)
> [C++][Dataset] Support null -> other type promotion in Dataset scanning
> -----------------------------------------------------------------------
>
> Key: ARROW-9147
> URL: https://issues.apache.org/jira/browse/ARROW-9147
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Joris Van den Bossche
> Priority: Major
> Labels: dataset, dataset-dask-integration
> Fix For: 1.0.0
>
>
> With regarding schema evolution / normalization, we support inserting nulls for a missing column or changing nullability, or normalizing column order, but we do not yet seem to support promotion of null type to any other type.
> Small python example:
> {code}
> In [11]: df = pd.DataFrame({"col": np.array([None, None, None, None], dtype='object')})
> ...: df.to_parquet("test_filter_schema.parquet", engine="pyarrow")
> ...:
> ...: import pyarrow.dataset as ds
> ...: dataset = ds.dataset("test_filter_schema.parquet", format="parquet", schema=pa.schema([("col", pa.int64())]))
> ...: dataset.to_table()
> ...
> ~/scipy/repos/arrow/python/pyarrow/_dataset.pyx in pyarrow._dataset.Dataset.to_table()
> ~/scipy/repos/arrow/python/pyarrow/_dataset.pyx in pyarrow._dataset.Scanner.to_table()
> ~/scipy/repos/arrow/python/pyarrow/error.pxi in pyarrow.lib.pyarrow_internal_check_status()
> ~/scipy/repos/arrow/python/pyarrow/error.pxi in pyarrow.lib.check_status()
> ArrowTypeError: fields had matching names but differing types. From: col: null To: col: int64
> {code}
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