suremarc commented on code in PR #9813:
URL: https://github.com/apache/arrow-datafusion/pull/9813#discussion_r1561563972
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datafusion/physical-expr/src/equivalence/mod.rs:
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@@ -35,14 +36,59 @@ pub use properties::{join_equivalence_properties,
EquivalenceProperties};
/// This function constructs a duplicate-free `LexOrderingReq` by filtering out
/// duplicate entries that have same physical expression inside. For example,
/// `vec![a Some(ASC), a Some(DESC)]` collapses to `vec![a Some(ASC)]`.
+///
+/// It will also filter out entries that are ordered if the next entry is;
+/// for instance, `vec![floor(a) Some(ASC), a Some(ASC)]` will be collapsed to
+/// `vec![a Some(ASC)]`.
pub fn collapse_lex_req(input: LexRequirement) -> LexRequirement {
let mut output = Vec::<PhysicalSortRequirement>::new();
for item in input {
if !output.iter().any(|req| req.expr.eq(&item.expr)) {
output.push(item);
}
}
- output
+ collapse_monotonic_lex_req(output)
+}
+
+/// This function constructs a normalized [`LexRequirement`] by filtering out
entries
+/// that are ordered if the next entry is.
+/// Used in `collapse_lex_req`
+fn collapse_monotonic_lex_req(input: LexRequirement) -> LexRequirement {
+ input
Review Comment:
I tried it, it seems challenging to avoid clones since the iteration looks
ahead at the next item. I think it could be done if we rewrote it as a fold or
reduce.
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