How to use eq_scalar with a dictionary-encoded array?

[RyanMarcus]

Hi folks,

I'm trying to use comparison::eq_scalar with a dictionary-encoded array. I can't seem to find the right type for the scalar. Here's an example:

use arrow2::{
    array::PrimitiveArray,
    compute::{cast, comparison},
    scalar::{DictionaryScalar, PrimitiveScalar},
};

fn main() {
    let arr = PrimitiveArray::<u64>::from_vec(vec![1, 2, 3, 1, 2, 3]);
    let dict_arr = cast::primitive_to_dictionary::<u64, u8>(&arr).unwrap();

    let scalar_val = PrimitiveScalar::from(Some(2_u64));

    // works
    println!("{:?}", comparison::eq_scalar(&arr, &scalar_val));

    // crashes: thread 'main' panicked at
    // []arrow2-0.18.0/src/compute/comparison/mod.rs:349:5: assertion `left == right`
    // failed left: Dictionary(UInt8, UInt64, false) right: UInt64
    println!("{:?}", comparison::eq_scalar(&dict_arr, &scalar_val));

    // crashes: thread 'main' panicked at
    // []]arrow2-0.18.0/src/compute/comparison/mod.rs:349:5: assertion `left == right`
    // failed left: UInt64 right: Dictionary(UInt8, UInt64, false)
    let scalar_dict_val: DictionaryScalar<u8> = DictionaryScalar::new(
        dict_arr.data_type().clone(),
        Some(Box::new(scalar_val.clone())),
    );
    println!("{:?}", comparison::eq_scalar(&dict_arr, &scalar_dict_val));
}

Comparing a dictionary array to a PrimitiveScalar triggers the assert at the top of the compare scalar macro. Using a DictionaryScalar passes the assert initially, but then this code calls the eq_scalar function recursively with the interior value of the DictionaryScalar, causing the same issue as when a PrimitiveScalar was used.

            Dictionary(key_type) => {
                match_integer_type!(key_type, |$T| {
                    let lhs = lhs.as_any().downcast_ref::<DictionaryArray<$T>>().unwrap();
                    let values = $op(lhs.values().as_ref(), rhs);

                    take_boolean(&values, lhs.keys())
                })
            }

What's the right way to use eq_scalar with a DictionaryArray?