Jefffrey commented on code in PR #22707:
URL: https://github.com/apache/datafusion/pull/22707#discussion_r3339196343
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datafusion/functions-aggregate-common/src/aggregate/count_distinct/native.rs:
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@@ -518,3 +519,85 @@ impl Accumulator for
Bitmap65536DistinctCountAccumulatorI16 {
size_of_val(self) + 8192
}
}
+
+/// Optimized COUNT DISTINCT accumulator for `Boolean` using two flags.
+///
+/// Tracks whether `false` and `true` have been observed; nulls are skipped.
+/// Result is always 0, 1, or 2.
+#[derive(Debug)]
+pub struct BooleanDistinctCountAccumulator {
+ seen: [bool; 2],
+}
+
+impl BooleanDistinctCountAccumulator {
+ pub fn new() -> Self {
+ Self { seen: [false; 2] }
+ }
+
+ #[inline]
+ fn count(&self) -> i64 {
+ self.seen.iter().filter(|&&b| b).count() as i64
+ }
+}
+
+impl Default for BooleanDistinctCountAccumulator {
+ fn default() -> Self {
+ Self::new()
+ }
+}
+
+impl Accumulator for BooleanDistinctCountAccumulator {
+ fn update_batch(&mut self, values: &[ArrayRef]) ->
datafusion_common::Result<()> {
+ if values.is_empty() {
+ return Ok(());
+ }
+
+ let arr = as_boolean_array(&values[0])?;
+ for value in arr.iter().flatten() {
+ self.seen[value as usize] = true;
+ if self.seen[0] && self.seen[1] {
+ break;
+ }
+ }
Review Comment:
We can probably be smarter with these:
- can bail earlier before checking input array if state already has seen both
- can use
[`has_true`](https://docs.rs/arrow/latest/arrow/array/struct.BooleanArray.html#method.has_true)
and
[`has_false`](https://docs.rs/arrow/latest/arrow/array/struct.BooleanArray.html#method.has_false)
instead of checking whole array
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