[jira] [Commented] (ARROW-3866) [Python] Column metadata is not transferred to tables in pyarrow

["Wes McKinney (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-3866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16705533#comment-16705533 ] 

Wes McKinney commented on ARROW-3866:
-------------------------------------

[~kszucs] could you have a look at this?

> [Python] Column metadata is not transferred to tables in pyarrow
> ----------------------------------------------------------------
>
>                 Key: ARROW-3866
>                 URL: https://issues.apache.org/jira/browse/ARROW-3866
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>            Reporter: Seb Fru
>            Priority: Major
>              Labels: features, newbie
>             Fix For: 0.12.0
>
>
> Hello everyone,
> transferring this from Github for Pyarrow. While working with pyarrow I noticed that field metadata does not get carried foreward when creating a table out of several columns. Is this intended behaviour or is there a way to add column metadata later on? The last command in my example does not return anything.
>  I also could not verify whether this data would be written to parquet later on, because I could not find a way to add field metadata directly to a table.
>  
> {code:java}
> >>>import pyarrow as pa
> >>>import pyarrow.parquet as pq 
> >>>arr1 = pa.array([1,2]) 
> >>>arr2 = pa.array([3,4]) 
> >>>field1 = pa.field('field1', pa.int64()) 
> >>>field2 = pa.field('field2', pa.int64()) 
> >>>field1 = field1.add_metadata({'foo1': 'bar1'}) 
> >>>field2 = field2.add_metadata({'foo2': 'bar2'}) 
> >>>field1.metadata {b'foo1': b'bar1'} 
> >>>field2.metadata {b'foo2': b'bar2'} 
> >>>col1 = pa.column(field1, arr1) 
> >>>col2 = pa.column(field2, arr2) 
> >>>col1.field.metadata {b'foo1': b'bar1'} 
> >>>tab = pa.Table.from_arrays([col1, col2]) 
> >>>tab pyarrow.Table field1: int64 field2: int64 
> >>>tab.column(0).field.metadata
> {code}



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