[jira] [Updated] (ARROW-9147) [C++][Dataset] Support null -> other type promotion in Dataset scanning

["Joris Van den Bossche (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-9147?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Joris Van den Bossche updated ARROW-9147:
-----------------------------------------
        Parent: ARROW-11003
    Issue Type: Sub-task  (was: Improvement)

> [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: Sub-task
>          Components: C++
>            Reporter: Joris Van den Bossche
>            Assignee: Ben Kietzman
>            Priority: Major
>              Labels: dataset, dataset-dask-integration, pull-request-available
>             Fix For: 2.0.0
>
>          Time Spent: 1h 40m
>  Remaining Estimate: 0h
>
> 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}



--
This message was sent by Atlassian Jira
(v8.3.4#803005)