jorgecarleitao commented on a change in pull request #1248:
URL: https://github.com/apache/arrow-rs/pull/1248#discussion_r800191885
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File path: arrow/src/compute/kernels/filter.rs
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@@ -119,17 +155,83 @@ impl<'a> Iterator for SlicesIterator<'a> {
}
}
+/// An iterator of `usize` whose index in [`BooleanArray`] is true
+///
+/// This provides the best performance on all but the least selective
predicates (which keep most
+/// / all rows), where the benefits of copying large runs instead favours
[`SlicesIterator`]
+struct IndexIterator<'a> {
+ current_chunk: u64,
+ chunk_offset: i64,
+ remaining: usize,
+ iter: UnalignedBitChunkIterator<'a>,
+}
+
+impl<'a> IndexIterator<'a> {
+ fn new(filter: &'a BooleanArray, len: usize) -> Self {
+ assert_eq!(filter.null_count(), 0);
+ let data = filter.data();
+ let chunks =
+ UnalignedBitChunk::new(&data.buffers()[0], data.offset(),
data.len());
+ let mut iter = chunks.iter();
+
+ let current_chunk = iter.next().unwrap_or(0);
+ let chunk_offset = -(chunks.lead_padding() as i64);
+
+ Self {
+ current_chunk,
+ chunk_offset,
+ remaining: len,
+ iter,
+ }
+ }
+}
+
+impl<'a> Iterator for IndexIterator<'a> {
+ type Item = usize;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ while self.remaining != 0 {
+ if self.current_chunk != 0 {
+ let bit_pos = self.current_chunk.trailing_zeros();
+ self.current_chunk ^= 1 << bit_pos;
+ self.remaining -= 1;
+ return Some((self.chunk_offset + bit_pos as i64) as usize);
+ }
+
+ // Must panic if exhausted early as trusted length iterator
+ self.current_chunk = self.iter.next().expect("IndexIterator
exhausted early");
+ self.chunk_offset += 64;
+ }
+ None
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (self.remaining, Some(self.remaining))
+ }
+}
+
+/// Counts the number of set bits in `filter`
fn filter_count(filter: &BooleanArray) -> usize {
Review comment:
not sure why this was/here here, but isn't this equal to `filter.len() -
filter.null_count()`?
EDIT: ah, maybe this is not true because null_count does not take the
offsets into account?
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