martin-g commented on code in PR #19571:
URL: https://github.com/apache/datafusion/pull/19571#discussion_r2657501800
##########
datafusion/functions/src/unicode/left.rs:
##########
@@ -139,14 +139,22 @@ fn left_impl<'a, T: OffsetSizeTrait, V:
ArrayAccessor<Item = &'a str>>(
n_array: &Int64Array,
) -> Result<ArrayRef> {
let iter = ArrayIter::new(string_array);
+ let mut chars_buf = Vec::new();
let result = iter
.zip(n_array.iter())
.map(|(string, n)| match (string, n) {
(Some(string), Some(n)) => match n.cmp(&0) {
Ordering::Less => {
- let len = string.chars().count() as i64;
+ // Collect chars once and reuse for both count and take
+ chars_buf.clear();
+ chars_buf.extend(string.chars());
+ let len = chars_buf.len() as i64;
+
Some(if n.abs() < len {
Review Comment:
minor improvement: calling .abs() on MIN will lead to problems (crash in dev
and wrapping in release).
i64::MIN is a corner case, so I guess no one will complain that it is not
supported here.
I also tried with `if n + len > 0` but then it was 3% slower on my machine.
```suggestion
Some(if n != i64::MIN && n.abs() < len {
```
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