[C++] Casting dictionary type to use different index type #27536
Description
It's currently not implemented to cast from one dictionary type to another dictionary type to change the index type.
Small example:
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())From https://stackoverflow.com/questions/66223730/how-to-change-column-datatype-with-pyarrow
Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: Niranda Perera / @nirandaperera
Related issues:
- [Python] Casting between dictionary types (is cloned by)
PRs and other links:
Note: This issue was originally created as ARROW-11673. Please see the migration documentation for further details.