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Add DictionaryArray::key function #1912

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merged 1 commit into from Jun 20, 2022
Merged

Add DictionaryArray::key function #1912

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22 changes: 22 additions & 0 deletions arrow/src/array/array_dictionary.rs
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Expand Up @@ -169,6 +169,17 @@ impl<'a, K: ArrowPrimitiveType> DictionaryArray<K> {
.iter()
.map(|key| key.map(|k| k.to_usize().expect("Dictionary index not usize")))
}

/// Return the value of `keys` (the dictionary key) at index `i`,
/// cast to `usize`, `None` if the value at `i` is `NULL`.
pub fn key(&self, i: usize) -> Option<usize> {
self.keys.is_valid(i).then(|| {
self.keys
.value(i)
.to_usize()
.expect("Dictionary index not usize")
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For most cases this unwrap won't panic, but do we need to maintain the same behavior with https://github.com/apache/arrow-datafusion/blob/080c32400ddfa2d45b5bebb820184eac8fd5a03a/datafusion/common/src/scalar.rs#L342-L358 ? If so the return type can either be Result<Option<_>> or Option<_>, I'm ok with both (hard to choose...).

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Panicking should be fine, it's a validation failure if the array contains negative indexes. TBH I keep meaning to change all these checked conversions to numeric casts (i.e. as), I wouldn't be surprised if this leads to non-trivial performance benefits.

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Filed #1918 to track

})
}
}

/// Constructs a `DictionaryArray` from an array data reference.
Expand Down Expand Up @@ -534,6 +545,17 @@ mod tests {
assert!(iter.next().is_none());
}

#[test]
fn test_dictionary_key() {
let keys = Int8Array::from(vec![Some(2), None, Some(1)]);
let values = StringArray::from(vec!["foo", "bar", "baz", "blarg"]);

let array = DictionaryArray::try_new(&keys, &values).unwrap();
assert_eq!(array.key(0), Some(2));
assert_eq!(array.key(1), None);
assert_eq!(array.key(2), Some(1));
}

#[test]
fn test_try_new() {
let values: StringArray = [Some("foo"), Some("bar"), Some("baz")]
Expand Down