[ARROW-3978] [C++] Implement hashing, dictionary-encoding for StructArray

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: C++
• Labels: query-engine
• External issue URL: https://github.com/apache/arrow/issues/20581
• Assignee: Unassigned
• Reporter: Wes McKinney
• Created: 09/Dec/18 21:30
• Updated: 11/Jan/23 07:30

Description

This is a central requirement for hash-aggregations such as

SELECT AGG_FUNCTION(expr)
FROM table
GROUP BY expr1, expr2, ...

The materialized keys in the GROUP BY section form a struct, which can be incrementally hashed to produce dictionary codes suitable for computing aggregates or any other purpose.

There are a few subtasks related to this, such as efficiently constructing a record (that can be hashed quickly) to identify each "row" in the struct. Maybe we should start with that first

Issue Links

• is a child of: ARROW-8894 [C++] C++ array kernels framework and execution buildout (umbrella issue)
• is a parent of: ARROW-8991 [C++][Compute] Add scalar_hash function