tlm365 commented on code in PR #14025:
URL: https://github.com/apache/datafusion/pull/14025#discussion_r1904999369
##########
datafusion/functions/src/unicode/reverse.rs:
##########
@@ -116,14 +115,23 @@ pub fn reverse<T: OffsetSizeTrait>(args: &[ArrayRef]) ->
Result<ArrayRef> {
}
}
-fn reverse_impl<'a, T: OffsetSizeTrait, V: ArrayAccessor<Item = &'a str>>(
+fn reverse_impl<'a, T: OffsetSizeTrait, V: StringArrayType<'a>>(
string_array: V,
) -> Result<ArrayRef> {
- let result = ArrayIter::new(string_array)
- .map(|string| string.map(|string: &str|
string.chars().rev().collect::<String>()))
- .collect::<GenericStringArray<T>>();
+ let mut builder: GenericStringBuilder<T> =
+ GenericStringBuilder::with_capacity(string_array.len(), 1024);
+
+ for string in string_array.iter() {
+ if let Some(s) = string {
+ let mut reversed = String::with_capacity(s.len());
Review Comment:
@simonvandel Thanks for reviewing
> I wonder if this allocation can be removed by using the Write impl? See
https://arrow.apache.org/rust/arrow/array/type.GenericStringBuilder.html#example-incrementally-writing-strings-with-stdfmtwrite
> Perhaps by iterating through the rev iterator, writing chars one at a time.
I tested this solution and the performance is not as good as this PR.
> If the above is slower, it could also be interesting to see if reusing the
String allocation with a clear() on every loop is faster
Indeed, this one is faster. I will update the code and provide benchmarks
shortly. TYSM ❤️
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