[jira] [Updated] (ARROW-9132) [C++] Support unique kernel for dictionary type

["Joris Van den Bossche (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-9132?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Joris Van den Bossche updated ARROW-9132:
-----------------------------------------
    Summary: [C++] Support unique kernel for dictionary type  (was: [Python] Support unique for dictionary type)

> [C++] Support unique kernel for dictionary type
> -----------------------------------------------
>
>                 Key: ARROW-9132
>                 URL: https://issues.apache.org/jira/browse/ARROW-9132
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: Python
>    Affects Versions: 0.17.1
>            Reporter: Dave Hirschfeld
>            Priority: Major
>             Fix For: 1.0.0
>
>
> Enabling [`strings_as_dictionary`](https://turbodbc.readthedocs.io/en/latest/pages/advanced_usage.html?highlight=strings_as_dictionary#obtaining-apache-arrow-result-sets) in `turbodbc` returns a `ChunkedArray` of `dictionary` type (IIUC).
> I'd like to enable this for better performance however it seems not all functionality is implemented for `dictionary` types? In particular, `unique` seems not to be implemented:
> {code}
> In [40]: nmi.__class__.mro()
> Out[40]: [pyarrow.lib.ChunkedArray, pyarrow.lib._PandasConvertible, object]
> In [41]: nmi.type
> Out[41]: DictionaryType(dictionary<values=string, indices=int32, ordered=0>)
> In [42]: nmi.unique()
> Traceback (most recent call last):
>   File "<ipython-input-42-0fcb7893d5c4>", line 1, in <module>
>     nmi.unique()
>   File "pyarrow\table.pxi", line 307, in pyarrow.lib.ChunkedArray.unique
>   File "pyarrow\error.pxi", line 106, in pyarrow.lib.check_status
> ArrowNotImplementedError: unique not implemented for dictionary<values=string, indices=int32, ordered=0>
> {code}
> It would be very useful if the `dictionary` type supported all the usual operations.



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