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https://issues.apache.org/jira/browse/ARROW-7087?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joris Van den Bossche resolved ARROW-7087.
------------------------------------------
Resolution: Fixed
Issue resolved by pull request 6127
[https://github.com/apache/arrow/pull/6127]
> [Python] Table Metadata disappear when we write a partitioned dataset
> ---------------------------------------------------------------------
>
> Key: ARROW-7087
> URL: https://issues.apache.org/jira/browse/ARROW-7087
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Affects Versions: 0.14.1
> Reporter: François Blanchard
> Assignee: François Blanchard
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.0.0
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> There is an unexpected behavior with the method
> *[write_to_dataset|https://github.com/apache/arrow/blob/10a3b716a5ca227c8d97e6f6b27976df14678263/python/pyarrow/parquet.py#L1373]*
> in *pyarrow/parquet.py*
> When we write a table that contains metadata then metadata are replaced by
> pandas metadata. This happens only if we defined *partition_cols*.
>
> To be more explicit here is an example code:
> {code:python}
> from pyarrow.parquet import write_to_dataset
> import pyarrow as pa
> import pyarrow.parquet as pd
> columnA = pa.array(['a', 'b', 'c'], type=pa.string())
> columnB = pa.array([1, 1, 2], type=pa.int32())
> # Build table from collumns
> table = pa.Table.from_arrays([columnA, columnB], names=['columnA',
> 'columnB'], metadata={'data': 'test'})
> print table.schema.metadata
> """
> Metadata is set as expected
> >> OrderedDict([('data', 'test')])
> """
> # Write table in parquet format partitioned per columnB
> write_to_dataset(table, '/path/to/test', partition_cols=['columnB'])
> # Load data from parquet files
> ds = pd.ParquetDataset('/path/to/test')
> load_table = pq.read_table(ds.pieces[0].path)
> print load_table.schema.metadata
> """
> Metadata with the key `data` is missing
> >> OrderedDict([('pandas', '{"creator": {"version": "0.14.1", "library":
> >> "pyarrow"}, "pandas_version": "0.22.0", "index_columns": [], "columns":
> >> [{"metadata": null, "field_name": "columnA", "name": "columnA",
> >> "numpy_type": "object", "pandas_type": "unicode"}], "column_indexes":
> >> []}')])
> """{code}
>
>
>
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