[ARROW-8383] [Rust] Easier random access to DictionaryArray keys and values

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.0.0
• Component/s: Rust
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/24567
• Assignee: Jörn Horstmann
• Reporter: Jörn Horstmann
• Created: 09/Apr/20 14:35
• Updated: 11/Jan/23 08:00
• Resolved: 31/Aug/20 14:26

Description

Currently it's not that clear how to acces DictionaryArray keys and values using random indices.

The `DictionaryArray::keys` method exposes an Iterator with an `nth` method, but this requires a mut reference and feels a little bit out of place compared to other methods of accessing arrow data.

Another alternative seems to be to use the `From<ArrayDataRef> for PrimitiveArray<T>` conversion like so `let keys : Int16Array = dictionary_array.data().into()`. This seems to work fine but is not easily discoverable and also needs to be done outside of any loops for performance reasons.

I'd like methods on `DictionaryArray` to directly get the key at some index

```
pub fn key(&self, i: usize) -> &K
```

Ideally I'd also like an easier way to directly access values at some index, at least when those are primitive or string types.

```
pub fn value(&self, i: usize) -> &T
```

I'm not sure how or if that would be possible to implement with rust generics.

 

Issue Links

• links to: GitHub Pull Request #8063