ClSlaid commented on code in PR #10460:
URL: https://github.com/apache/datafusion/pull/10460#discussion_r1597540519
##########
datafusion/optimizer/src/replace_distinct_aggregate.rs:
##########
@@ -88,60 +94,72 @@ impl OptimizerRule for ReplaceDistinctWithAggregate {
input,
schema,
})) => {
+ let expr_cnt = on_expr.len();
+
// Construct the aggregation expression to be used to fetch
the selected expressions.
- let aggr_expr = select_expr
- .iter()
- .map(|e| {
- Expr::AggregateFunction(AggregateFunction::new(
- AggregateFunctionFunc::FirstValue,
- vec![e.clone()],
- false,
- None,
- sort_expr.clone(),
- None,
- ))
- })
- .collect::<Vec<Expr>>();
+ let aggr_expr =
vec![Expr::AggregateFunction(AggregateFunction::new(
+ AggregateFunctionFunc::FirstValue,
+ select_expr,
+ false,
+ None,
+ sort_expr.clone(),
+ None,
+ ))];
Review Comment:
> The difference is that the `select_expr.iter()...` makes a `vec` with the
same number of elements as `select_expr `
>
> To avoid a clone, perhaps you can use `into_iter` instead of `iter`, like
>
> ```rust
> let aggr_expr = select_expr
> .into_iter() // <---- Use into_iter() here
> .map(|e| {
> Expr::AggregateFunction(AggregateFunction::new(
> AggregateFunctionFunc::FirstValue,
> vec![e], // <--- to avoid a clone here
> false,
> None,
> sort_expr.clone(),
> None,
> ))
> })
> .collect::<Vec<Expr>>();
> ```
What bothers me most is that I cannot avoid cloning `sort_expr`. However, it
looks like the only way to make it correct.
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