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

["Igor Yastrebov (Jira)" <ji...@apache.org>]

Igor Yastrebov created ARROW-6578:
-------------------------------------

             Summary: [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: Python
    Affects Versions: 0.14.1
            Reporter: Igor Yastrebov


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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