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https://issues.apache.org/jira/browse/ARROW-8221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17229957#comment-17229957
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Joris Van den Bossche commented on ARROW-8221:
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[~westonpace] do you have an example? Normally, missing columns in one of the
files is something that should be supported already (they get filled with
nulls).
{code}
In [1]: table = pa.table({'a': [1, 2, 3]})
In [2]: import pyarrow.dataset as ds
In [3]: ds.write_dataset(table, "test_columns", format="parquet")
In [6]: ds.dataset("test_columns").to_table().to_pandas()
Out[6]:
a
0 1
1 2
2 3
In [7]: ds.dataset("test_columns", schema=pa.schema([('a', 'int64'), ('b',
'float64')])).to_table().to_pandas()
Out[7]:
a b
0 1 NaN
1 2 NaN
2 3 NaN
{code}
> [Python][Dataset] Expose schema inference / validation options in the factory
> -----------------------------------------------------------------------------
>
> Key: ARROW-8221
> URL: https://issues.apache.org/jira/browse/ARROW-8221
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Python
> Reporter: Joris Van den Bossche
> Assignee: Joris Van den Bossche
> Priority: Major
> Labels: dataset
> Fix For: 3.0.0
>
>
> ARROW-8058 added options related to schema inference / validation for the
> Dataset factory. We should expose this in Python in the {{dataset(..)}}
> factory function:
> - Add ability to pass a user-specified schema with a {{schema}} keyword,
> instead of inferring the schema from (one of) the files (to be passed to the
> factory finish method)
> - Add {{validate_schema}} option to toggle whether the schema is validated
> against the actual files or not.
> - Expose in some way the number of fragments to be inspected when inferring
> or validating the schema. Not sure yet what the best API for this would be.
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