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Improve default implementation of Array::is_nullable #6721

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Nov 20, 2024
Merged

Improve default implementation of Array::is_nullable #6721

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e1fb10c
Improve default implementation of Array::is_nullable
findepi Nov 12, 2024
9e6fbf8
Implement efficient DictionaryArray::logical_null_count
findepi Nov 16, 2024
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20 changes: 20 additions & 0 deletions arrow-array/src/array/dictionary_array.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -749,6 +749,26 @@ impl<T: ArrowDictionaryKeyType> Array for DictionaryArray<T> {
}
}

fn logical_null_count(&self) -> usize {
match (self.keys.nulls(), self.values.logical_nulls()) {
(None, None) => 0,
(Some(key_nulls), None) => key_nulls.null_count(),
(None, Some(value_nulls)) => self
.keys
.values()
.iter()
.filter(|k| value_nulls.is_null(k.as_usize()))
.count(),
(Some(key_nulls), Some(value_nulls)) => self
.keys
.values()
.iter()
.enumerate()
.filter(|(idx, k)| key_nulls.is_null(*idx) || value_nulls.is_null(k.as_usize()))
.count(),
}
}

fn is_nullable(&self) -> bool {
!self.is_empty() && (self.nulls().is_some() || self.values.is_nullable())
}
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3 changes: 1 addition & 2 deletions arrow-array/src/array/mod.rs
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Expand Up @@ -317,8 +317,7 @@ pub trait Array: std::fmt::Debug + Send + Sync {
/// even if the nulls present in [`DictionaryArray::values`] are not referenced by any key,
/// and therefore would not appear in [`Array::logical_nulls`].
fn is_nullable(&self) -> bool {
// TODO this is not necessarily perfect default implementation, since null_count() and logical_null_count() are not always equivalent
self.null_count() != 0
self.logical_null_count() != 0
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Can we provide alternative implementations DictionaryArray and UnionArray as part of this, currently this will significantly regress performance for them

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the logical_null_count implementation should obviously be consistent with logical_nulls implementation, so let's do #6740 first

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i added explicit implementation of DictionaryArray::logical_null_count
i am not sure what to do about UnionArray. UnionArray::logical_nulls has non trivial logic. Can you please advise how this should be approached the best way? should I just copy that function?

cc @alamb

}

/// Returns the total number of bytes of memory pointed to by this array.
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