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https://issues.apache.org/jira/browse/ARROW-9132?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wes McKinney updated ARROW-9132:
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Summary: [C++] Implement hash kernels for dictionary data with constant
dictionaries (was: [C++] Support unique kernel for dictionary type)
> [C++] Implement hash kernels for dictionary data with constant dictionaries
> ---------------------------------------------------------------------------
>
> Key: ARROW-9132
> URL: https://issues.apache.org/jira/browse/ARROW-9132
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++, Python
> Affects Versions: 0.17.1
> Reporter: Dave Hirschfeld
> Priority: Major
> Fix For: 2.0.0
>
>
> 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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