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Consolidate filter_null_mask into FilterPredicate::filter_nulls #10049

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Consolidate filter_null_mask into FilterPredicate::filter_nulls #10049

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57 changes: 18 additions & 39 deletions arrow-select/src/filter.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -410,19 +410,31 @@ impl FilterPredicate {
self.count
}

/// Filters the given `nulls` buffer using this predicate.
/// Computes a new [`NullBuffer`] by applying this predicate to `nulls`.
///
/// Returns `None` when there is nothing to track in the output, either
/// because the input `nulls` was `None`, the input had no nulls, or the
/// filtered result has no nulls. Otherwise returns the filtered
/// [`NullBuffer`] with its precomputed null count.
pub fn filter_nulls(&self, nulls: Option<&NullBuffer>) -> Option<NullBuffer> {
let (null_count, nulls) = filter_null_mask(nulls, self)?;
let buffer = BooleanBuffer::new(nulls, 0, self.count);
let nulls = nulls?;
if nulls.null_count() == 0 {
return None;
}

let nulls = filter_bits(nulls.inner(), self);
// The filtered `nulls` has a length of `self.count` bits and therefore
// the null count is this minus the number of valid bits
let null_count = self.count - nulls.count_set_bits_offset(0, self.count);

if null_count == 0 {
return None;
}

let buffer = BooleanBuffer::new(nulls, 0, self.count);
debug_assert_eq!(null_count, buffer.len() - buffer.count_set_bits());
// SAFETY: `filter_null_mask` derived `null_count` from `buffer`, so it
// matches the number of unset bits as required by `new_unchecked`.
// SAFETY: `null_count` was derived from `buffer` above, so it matches
// the number of unset bits as required by `new_unchecked`.
Some(unsafe { NullBuffer::new_unchecked(buffer, null_count) })
}
}
Expand Down Expand Up @@ -569,33 +581,6 @@ where
RunArray::try_new(&run_ends, &values)
}

/// Computes a new null mask for `data` based on `predicate`
///
/// If the predicate selected no null-rows, returns `None`, otherwise returns
/// `Some((null_count, null_buffer))` where `null_count` is the number of nulls
/// in the filtered output, and `null_buffer` is the filtered null buffer
///
fn filter_null_mask(
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@alamb alamb Jun 2, 2026

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The idea is to just inline this into the FilterPredicate::filter_nulls to make the API simpler (as it already requires a predicate: &FilterPredicate anyway)

nulls: Option<&NullBuffer>,
predicate: &FilterPredicate,
) -> Option<(usize, Buffer)> {
let nulls = nulls?;
if nulls.null_count() == 0 {
return None;
}

let nulls = filter_bits(nulls.inner(), predicate);
// The filtered `nulls` has a length of `predicate.count` bits and
// therefore the null count is this minus the number of valid bits
let null_count = predicate.count - nulls.count_set_bits_offset(0, predicate.count);

if null_count == 0 {
return None;
}

Some((null_count, nulls))
}

/// Filter the packed bitmask `buffer`, with `predicate` starting at bit offset `offset`
fn filter_bits(buffer: &BooleanBuffer, predicate: &FilterPredicate) -> Buffer {
let src = buffer.values();
Expand Down Expand Up @@ -940,13 +925,7 @@ fn filter_struct(
.map(|column| filter_array(column, predicate))
.collect::<Result<_, _>>()?;

let nulls = if let Some((null_count, nulls)) = filter_null_mask(array.nulls(), predicate) {
let buffer = BooleanBuffer::new(nulls, 0, predicate.count);

Some(unsafe { NullBuffer::new_unchecked(buffer, null_count) })
} else {
None
};
let nulls = predicate.filter_nulls(array.nulls());

Ok(unsafe {
StructArray::new_unchecked_with_length(
Expand Down
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