[ARROW-17963] [C++] Implement casting to dictionary type (dictionary_encode as a cast)

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Fix Version/s: 11.0.0
• Component/s: C++
• Labels: Kernels
• External issue URL: https://github.com/apache/arrow/issues/33171

Language

C++

• Assignee: Unassigned
• Reporter: Will Jones
• Created: 07/Oct/22 16:50
• Updated: 11/Jan/23 11:57

Description

We can cast dictionary(string, X) to string, but not the other way around.

> Array$create(c("a", "b"))$cast(dictionary(int32(), string()))
Error: NotImplemented: Unsupported cast from string to dictionary using function cast_dictionary
/Users/willjones/Documents/arrows/arrow/cpp/src/arrow/compute/function.cc:249  func.DispatchBest(&in_types)

> Array$create(as.factor(c("a", "b")))$cast(string())
Array
<string>
[
  "a",
  "b"
]

Issue Links

• relates to: ARROW-13103 [C++][Python] Allow to specify a dictionary type for dictionary_encode() function