alamb opened a new issue #672:
URL: https://github.com/apache/arrow-rs/issues/672
**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:
```rust
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):
```rust
impl DictionaryArray<K: ArrowDictionaryKeyType> {
// return the index into the dictionary values for array@index as well
// as the dictioanry values
#[inline]
fn dict_value(
self:
index: usize,
) -> Result<(&ArrayRef, usize)>
{
// look up the index in the values dictionary
let keys_col = self.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()
))
})?;
Ok((self.values(), values_index))
}
```
**Describe alternatives you've considered**
**Additional context**
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