alamb commented on pull request #984:
URL: https://github.com/apache/arrow-rs/pull/984#issuecomment-992692480
So I messed around with this some more. The key thing I kept hitting was
that the comparisons to the dictionary values effectively needed to be "dynamic"
Here is one approach that we might be able to use (and skip the specialized
`eq_dict_scalar` entirely).
```rust
/// Perform `left == right` operation on an array and a numeric scalar
/// value. Supports PrimtiveArrays, and DictionaryArrays that have primitive
values
pub fn eq_dyn_scalar<T>(
left: &dyn Array,
right: T::Native,
) -> Result<BooleanArray>
where
T: ArrowNumericType,
{
#[cfg(not(feature = "simd"))]
println!("{}", std::any::type_name::<T>());
match left.data_type() {
DataType::UInt8 => {
// horrible (?) way to get a u8
let right: u8 = right.to_usize()
.and_then(|right| right.try_into().ok())
.ok_or_else(|| ArrowError::ComputeError(format!("Can not
convert {:?} to u8 for comparison with UInt8Array", right)))?;
eq_scalar::<UInt8Type>(as_primitive::<UInt8Type>(left), right)
}
DataType::UInt16 => {
// horrible (?) way to get a u16
let right: u16 = right.to_usize()
.and_then(|right| right.try_into().ok())
.ok_or_else(|| ArrowError::ComputeError(format!("Can not
convert {:?} to u16 for comparison with UInt16Array", right)))?;
eq_scalar::<UInt16Type>(as_primitive::<UInt16Type>(left), right)
}
// TODO other primitive array types
DataType::Dictionary(key_type, value_type) => {
match key_type.as_ref() {
DataType::UInt8 => {
let left = as_dictionary::<UInt8Type>(left);
unpack_dict_comparison(left,
eq_dyn_scalar::<T>(left.values().as_ref(), right)?)
}
// TODO fill out the rest of the key types here
_ => todo!()
}
}
// TODO macroize / fill out rest of primitive dispatch
_ => todo!()
}
}
```
The downside is you still need type annotations at the callsite:
```rust
#[test]
fn test_dict_eq_scalar() {
...
let array = builder.finish();
// still need the UInt8Type annotations
let a_eq = eq_dyn_scalar::<UInt8Type>(&array, 123u8).unwrap();
assert_eq!(
a_eq,
BooleanArray::from(vec![Some(true), None, Some(false)])
);
}
```
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