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refactor character_length impl by unifying null handling logic #16877

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refactor character_length impl by unifying null handling logic #16877

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aa87260
refactor character_length impl by unifying null handling logic
waynexia Jul 23, 2025
74035bc
safety comment
waynexia Jul 23, 2025
c2f2326
maybe work?
waynexia Jul 27, 2025
28f66a1
fix clippy
waynexia Jul 27, 2025
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41 changes: 8 additions & 33 deletions datafusion/functions/src/unicode/character_length.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,56 +136,31 @@ where
// string is ASCII only is relatively cheap.
// If strings are ASCII only, count bytes instead.
let is_array_ascii_only = array.is_ascii();
let array = if array.null_count() == 0 {
let nulls = array.nulls().cloned();
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Is the idea to remove the no-nulls optimization because it doesn't make things faster?

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I think avoiding the null check (array.is_null(i)) makes things faster and it seems we don't need 0 as we always cloned array.nulls().cloned()

let array = {
if is_array_ascii_only {
let values: Vec<_> = (0..array.len())
.map(|i| {
let value = array.value(i);
// Safety: we are iterating with array.len() so the index is always valid
let value = unsafe { array.value_unchecked(i) };
T::Native::usize_as(value.len())
})
.collect();
PrimitiveArray::<T>::new(values.into(), None)
PrimitiveArray::<T>::new(values.into(), nulls)
} else {
let values: Vec<_> = (0..array.len())
.map(|i| {
let value = array.value(i);
// Safety: we are iterating with array.len() so the index is always valid
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Another idea here is if you know the values are always ascii, you can avoid making a &str at all -- and instead simply compute the character lengths based on the offsets array (for StringArray and LargeStringArray) or the views for `StringViewArray)

let value = unsafe { array.value_unchecked(i) };
if value.is_ascii() {
T::Native::usize_as(value.len())
} else {
T::Native::usize_as(value.chars().count())
}
})
.collect();
PrimitiveArray::<T>::new(values.into(), None)
PrimitiveArray::<T>::new(values.into(), nulls)
}
} else if is_array_ascii_only {
let values: Vec<_> = (0..array.len())
.map(|i| {
if array.is_null(i) {
T::default_value()
} else {
let value = array.value(i);
T::Native::usize_as(value.len())
}
})
.collect();
PrimitiveArray::<T>::new(values.into(), array.nulls().cloned())
} else {
let values: Vec<_> = (0..array.len())
.map(|i| {
if array.is_null(i) {
T::default_value()
} else {
let value = array.value(i);
if value.is_ascii() {
T::Native::usize_as(value.len())
} else {
T::Native::usize_as(value.chars().count())
}
}
})
.collect();
PrimitiveArray::<T>::new(values.into(), array.nulls().cloned())
};

Ok(Arc::new(array))
Expand Down