2010YOUY01 commented on code in PR #14025:
URL: https://github.com/apache/datafusion/pull/14025#discussion_r1906203641
##########
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:
I noticed `get_array_memory_size()` will overestimate
[source](https://github.com/apache/arrow-rs/blob/4f1f6e57c568fae8233ab9da7d7c7acdaea4112a/arrow-array/src/array/byte_view_array.rs#L600-L607),
also many other string function is not using the accurate estimation
I think it's okay to keep it simple and use the default size now, perhaps we
can introduce a function to calculate only payload size in the future, and make
estimation correct for all usages of `GenericStringBuilder`. Thank you for the
experiment.
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