Jefffrey commented on code in PR #19496:
URL: https://github.com/apache/datafusion/pull/19496#discussion_r2659448260
##########
datafusion/functions-window/src/nth_value.rs:
##########
@@ -519,6 +467,87 @@ impl PartitionEvaluator for NthValueEvaluator {
}
}
+impl NthValueEvaluator {
+ fn valid_index(&self, array: &ArrayRef, range: &Range<usize>) ->
Option<usize> {
+ let n_range = range.end - range.start;
+ if self.ignore_nulls {
+ // Calculate valid indices, inside the window frame boundaries.
+ let slice = array.slice(range.start, n_range);
+ if let Some(nulls) = slice.nulls() {
+ return match self.state.kind {
+ NthValueKind::First => {
+ nulls.valid_indices().next().map(|idx| idx +
range.start)
+ }
+ NthValueKind::Last => {
+ nulls.valid_indices().last().map(|idx| idx +
range.start)
+ }
+ NthValueKind::Nth => {
+ match self.n.cmp(&0) {
+ Ordering::Greater => {
+ // SQL indices are not 0-based.
+ let index = (self.n as usize) - 1;
+ nulls
+ .valid_indices()
+ .nth(index)
+ .map(|idx| idx + range.start)
+ }
+ Ordering::Less => {
+ let reverse_index = (-self.n) as usize;
+ if n_range < reverse_index {
+ // Outside the range, return NULL to avoid
allocating
+ // for the sliding window that will be
discarded in the end.
+ return None;
+ }
+ let mut window =
VecDeque::with_capacity(reverse_index);
Review Comment:
I think if we do something like this it can work without needing a separate
container?
```rust
Ordering::Less => {
let reverse_index = (-self.n) as usize;
let total_len = nulls.len();
let null_count = nulls.null_count();
let valid_indices_len = total_len - null_count;
if reverse_index > valid_indices_len {
return None;
}
nulls
.valid_indices()
.nth(valid_indices_len - reverse_index)
.map(|idx| idx + offset)
}
```
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