[GitHub] [arrow-rs] alamb commented on pull request #984: Add comparison kernels for DictionaryArray

[GitBox <gi...@apache.org>]

alamb commented on pull request #984:
URL: https://github.com/apache/arrow-rs/pull/984#issuecomment-989085691


   
   > one thing i noticed is that it doesnt seem there is way to create a DictionaryArray from a vec of scalars like you can with a vec of str slices.
   
   You can create `DictionaryArrays` from `&str`  using `FromIter` as shown in https://docs.rs/arrow/6.3.0/arrow/array/struct.DictionaryArray.html
   
   ```
   use arrow::array::{DictionaryArray, Int8Array};
   use arrow::datatypes::Int8Type;
   let test = vec!["a", "a", "b", "c"];
   let array : DictionaryArray<Int8Type> = test.iter().map(|&x| if x == "b" {None} else {Some(x)}).collect();
   assert_eq!(array.keys(), &Int8Array::from(vec![Some(0), Some(0), None, Some(1)]));
   ```
   
   There isn't an equivalent syntax for other scalar types (e.g. `u32`, `u64`, etc) though we could add them


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