Add a way to get the dictionary index and values array reference #672
Description
Is your feature request related to a problem or challenge? Please describe what you are trying to do.
To work with the value of a dictionary array at a particular index, the following pattern shows up many times in the arrow-rs and datafusion codebase:
fn do_something <K: ArrowDictionaryKeyType>(
array: &ArrayRef,
index: usize,
) -> Result<Self> {
let dict_array = array.as_any().downcast_ref::<DictionaryArray<K>>().unwrap();
// look up the index in the values dictionary
let keys_col = dict_array.keys();
let values_index = keys_col.value(index).to_usize().ok_or_else(|| {
DataFusionError::Internal(format!(
"Can not convert index to usize in dictionary of type creating group by value {:?}",
keys_col.data_type()
))
})?;
// do actual work with dict_array.values and values_index
// ...
}
}Repeating this code "find the index" code is tedious
Describe the solution you'd like
Add a function such as the following on to DictionaryArray (would love suggestions about better names):
impl DictionaryArray<K: ArrowDictionaryKeyType> {
// return the index into the dictionary values for array@index as well
// as the dictionary values
#[inline]
fn dict_value(
self:
index: usize,
) -> Result<(&ArrayRef, Option<usize>)>
{
// look up the index in the values dictionary
let keys_col = self.keys();
if !keyd_col.is_valid(index) {
return Ok((self.values(), None));
}
let values_index = keys_col.value(index).to_usize().ok_or_else(|| {
DataFusionError::Internal(format!(
"Can not convert index to usize in dictionary of type creating group by value {:?}",
keys_col.data_type()
))
})?;
Ok((self.values(), Some(values_index)))
}Describe alternatives you've considered
Additional context