[jira] [Assigned] (ARROW-11673) [C++] Casting dictionary type to use different index type

["Eduardo Ponce (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-11673?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Eduardo Ponce reassigned ARROW-11673:
-------------------------------------

    Assignee: Eduardo Ponce

> [C++] Casting dictionary type to use different index type
> ---------------------------------------------------------
>
>                 Key: ARROW-11673
>                 URL: https://issues.apache.org/jira/browse/ARROW-11673
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Joris Van den Bossche
>            Assignee: Eduardo Ponce
>            Priority: Major
>
> It's currently not implemented to cast from one dictionary type to another dictionary type to change the index type. 
> Small example:
> {code}
> In [2]: arr = pa.array(['a', 'b', 'a']).dictionary_encode()
> In [3]: arr.type
> Out[3]: DictionaryType(dictionary<values=string, indices=int32, ordered=0>)
> In [5]: arr.cast(pa.dictionary(pa.int8(), pa.string()))
> ...
> ArrowNotImplementedError: Unsupported cast from dictionary<values=string, indices=int32, ordered=0> to dictionary<values=string, indices=int8, ordered=0> (no available cast function for target type)
> ../src/arrow/compute/cast.cc:112  GetCastFunctionInternal(cast_options->to_type, args[0].type().get())
> {code}
> From https://stackoverflow.com/questions/66223730/how-to-change-column-datatype-with-pyarrow



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