[ARROW-12632] [C++][Dataset][Compute] Add support for dictionary_encode to Expression

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 4.0.0
• Component/s: C++
• Labels: dataset
• External issue URL: https://github.com/apache/arrow/issues/28384
• Assignee: Unassigned
• Reporter: Ben Kietzman
• Created: 03/May/21 15:35
• Updated: 11/Jan/23 08:27

Description

dictionary_encode should be usable in the context of ExecuteScalarExpression, but is not currently supported because it requires mutable state (the hash table). Currently scanning assumes that Expression state will not be mutated so only one instance is initialized and is shared between all threads of execution. Supporting dictionary_encode will require adding support for multiple states to Expression and usage of that by dataset scans.