[Python] Casting between dictionary types

[asfimport]

Casting between dictionary types isn't implemented. It leads to boilerplate code.
 

import pyarrow as pa

dt = pa.array([b"foo", b"bar", b"baz", b"bar", b"baz", b"bar"], type=pa.binary())
dictionary = dt.dictionary_encode()
print(dictionary.type)
# dictionary<values=binary, indices=int32, ordered=0>
pc.cast(dictionary, pa.dictionary(index_type=pa.int8(), value_type=pa.binary()), safe=False)

pyarrow.lib.ArrowNotImplementedError: Unsupported cast from dictionary<values=binary, indices=int32, ordered=0> to dictionary using function cast_dictionary

Reporter: Andrei Nesterov

Related issues:

• [C++] Casting dictionary type to use different index type (is a clone of)
• [C++][Python] Allow to specify a dictionary type for dictionary_encode() function (is related to)

_{Note: This issue was originally created as ARROW-13102. Please see the migration documentation for further details.}

[asfimport]

Andrei Nesterov:
The original problem described in ARROW-13103.

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
For casting to dictionary with another index type, this is covered in ARROW-11673. Is that your goal here, or also to cast to another values type?

[asfimport]

Andrei Nesterov:
I think so, thank you.