tlm365 commented on code in PR #14025:
URL: https://github.com/apache/datafusion/pull/14025#discussion_r1905010563
##########
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);
Review Comment:
@2010YOUY01 Thanks for reviewing,
> I think we can use the actual data size here for pre-allocation, instead
of a constant 1024, the complexity of adding another argument for array size
seems reasonable
I agree that it would be better if we could pre-allocate the actual data
size here, but I think it's difficult to compute accurately - it depends on
context. Keeping it simple here seems reasonable as well.
Currently `GenericStringBuilder` have `new` and `with_capacity` to init new
builder, and 1024 is default size if we using `GenericStringBuilder::new`
([ref](https://github.com/apache/arrow-rs/blob/4f1f6e57c568fae8233ab9da7d7c7acdaea4112a/arrow-array/src/builder/generic_bytes_builder.rs#L39-L41))
that's why I choose 1024 here.
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