[ARROW-13136] [C++] Add a "coalesce" variadic scalar kernel

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 5.0.0
• Component/s: C++
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/28837
• Assignee: David Li
• Reporter: Ian Cook
• Created: 21/Jun/21 15:53
• Updated: 11/Jan/23 08:31
• Resolved: 19/Jul/21 17:45

Description

Add a variadic scalar compute kernel that works like the SQL coalesce function. It should take arbitrarily many inputs of the same or compatible types and process them row-wise, returning the first non-null value in each row, or returning null if there are no non-null values in the row. 

For example, in the case of 3 integer-type input arrays, this would take inputs:

Array<int32>         Array<int32>         Array<int32>
[                    [                    [
  null,                2,                   3,
  4,                   null,                6,
  null,                null,                9,
  null                 null                 null
]                    ]                    ]

and return output:

Array<int32>
[ 
  2,
  4,
  9,
  null
] 

This should accept scalars and recycle their values.

Issue Links

• fixes: ARROW-13368 [C++][Doc] Rename project to make_struct in docs
• is depended upon by: ARROW-13201 [R] Add binding for coalesce()
• is duplicated by: ARROW-7179 [C++][Compute] Consolidate fill_null and coalesce
• is related to: ARROW-13390 [C++] Improve type support for 'coalesce' kernel
• links to: GitHub Pull Request #10608