[jira] [Updated] (ARROW-6578) [Python] Casting int64 to string columns

["Antoine Pitrou (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-6578?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Antoine Pitrou updated ARROW-6578:
----------------------------------
    Component/s: C++

> [Python] Casting int64 to string columns
> ----------------------------------------
>
>                 Key: ARROW-6578
>                 URL: https://issues.apache.org/jira/browse/ARROW-6578
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++, Python
>    Affects Versions: 0.14.1
>            Reporter: Igor Yastrebov
>            Priority: Major
>
> I wanted to cast a list of a tables to the same schema so I could use concat_tables later. However, I encountered ArrowNotImplementedError:
> {code:java}
> ---------------------------------------------------------------------------
> ArrowNotImplementedError                  Traceback (most recent call last)
> <ipython-input-11-bd4916c221bf> in <module>
> ----> 1 list_tb = [i.cast(mts_schema, safe = True) for i in list_tb]
> <ipython-input-11-bd4916c221bf> in <listcomp>(.0)
> ----> 1 list_tb = [i.cast(mts_schema, safe = True) for i in list_tb]
> ~\AppData\Local\Continuum\miniconda3\envs\cyclone\lib\site-packages\pyarrow\table.pxi in itercolumns()
> ~\AppData\Local\Continuum\miniconda3\envs\cyclone\lib\site-packages\pyarrow\table.pxi in pyarrow.lib.Column.cast()
> ~\AppData\Local\Continuum\miniconda3\envs\cyclone\lib\site-packages\pyarrow\error.pxi in pyarrow.lib.check_status()
> ArrowNotImplementedError: No cast implemented from int64 to string
> {code}
> Some context: I want to read and concatenate a bunch of csv files that come from partitioning of the same table. Using cast after reading csv is usually significantly faster than specifying column_types in ConvertOptions. There are string columns that are mostly populated with integer-like values so a particular file can have an integer-only column. This situation is rather common so having an option to cast int64 column to string column would be helpful.
>  



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