korowa commented on code in PR #8721:
URL: https://github.com/apache/arrow-datafusion/pull/8721#discussion_r1441602644
##########
datafusion/physical-expr/src/aggregate/count_distinct.rs:
##########
@@ -192,6 +262,164 @@ impl Accumulator for DistinctCountAccumulator {
}
}
+#[derive(Debug)]
+struct NativeDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send,
+ T::Native: Eq + Hash,
+{
+ values: HashSet<T::Native, RandomState>,
+}
+
+impl<T> NativeDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send,
+ T::Native: Eq + Hash,
+{
+ fn new() -> Self {
+ Self {
+ values: HashSet::default(),
+ }
+ }
+}
+
+impl<T> Accumulator for NativeDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send + Debug,
+ T::Native: Eq + Hash,
+{
+ fn state(&self) -> Result<Vec<ScalarValue>> {
+ let arr = Arc::new(PrimitiveArray::<T>::from_iter_values(
+ self.values.iter().cloned(),
+ )) as ArrayRef;
+ let list = Arc::new(array_into_list_array(arr)) as ArrayRef;
+ Ok(vec![ScalarValue::List(list)])
+ }
+
+ fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
+ if values.is_empty() {
+ return Ok(());
+ }
+
+ let arr = as_primitive_array::<T>(&values[0])?;
+ arr.iter().for_each(|value| {
+ if let Some(value) = value {
+ self.values.insert(value);
+ }
+ });
+
+ Ok(())
+ }
+
+ fn merge_batch(&mut self, states: &[ArrayRef]) -> Result<()> {
+ if states.is_empty() {
+ return Ok(());
+ }
+ assert_eq!(
+ states.len(),
+ 1,
+ "count_distinct states must be single array"
+ );
+
+ let arr = as_list_array(&states[0])?;
+ arr.iter().try_for_each(|maybe_list| {
+ if let Some(list) = maybe_list {
+ let list = as_primitive_array::<T>(&list)?;
+ self.values.extend(list.values())
+ };
+ Ok(())
+ })
+ }
+
+ fn evaluate(&self) -> Result<ScalarValue> {
+ Ok(ScalarValue::Int64(Some(self.values.len() as i64)))
+ }
+
+ fn size(&self) -> usize {
+ std::mem::size_of_val(self)
+ + std::mem::size_of_val(&self.values)
+ + (std::mem::size_of::<T::Native>() * self.values.capacity())
+ }
+}
+
+#[derive(Debug)]
+struct FloatDistinctCountAccumulator<T>
+where
+ T: ArrowPrimitiveType + Send,
+{
+ values: HashSet<Hashable<T::Native>, RandomState>,
Review Comment:
I might be wrong, but don't we need smth like
[specialization](https://rust-lang.github.io/rfcs/1210-impl-specialization.html)
for this? It would allow to have different implementations of eq + hash for
`Hashable` depending on generic bounds -- but it doesn't seem to be stable now
:thinking:
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