[GitHub] [arrow] Dandandan commented on a change in pull request #8836: ARROW-10808: [Rust][DataFusion] Support nested expressions in aggregations.

[GitBox <gi...@apache.org>]

Dandandan commented on a change in pull request #8836:
URL: https://github.com/apache/arrow/pull/8836#discussion_r536394633



##########
File path: rust/datafusion/src/sql/utils.rs
##########
@@ -0,0 +1,305 @@
+use crate::error::{DataFusionError, Result};
+use crate::logical_plan::{Expr, LogicalPlan};
+use arrow::datatypes::Schema;
+
+/// Resolves an `Expr::Wildcard` to a collection of `Expr::Column`'s.
+pub(crate) fn expand_wildcard(expr: &Expr, schema: &Schema) -> Vec<Expr> {
+    match expr {
+        Expr::Wildcard => schema
+            .fields()
+            .iter()
+            .map(|f| Expr::Column(f.name().to_string()))
+            .collect::<Vec<Expr>>(),
+        _ => vec![expr.clone()],
+    }
+}
+
+/// Collect all deeply nested `Expr::AggregateFunction` and
+/// `Expr::AggregateUDF`. They are returned in order of occurrence (depth
+/// first), with duplicates omitted.
+pub(crate) fn find_aggregate_exprs(exprs: &Vec<Expr>) -> Vec<Expr> {
+    find_exprs_in_exprs(exprs, &|nested_expr| match nested_expr {
+        Expr::AggregateFunction { .. } | Expr::AggregateUDF { .. } => true,
+        _ => false,
+    })
+}
+
+/// Collect all deeply nested `Expr::Column`'s. They are returned in order of
+/// appearance (depth first), with duplicates omitted.
+pub(crate) fn find_column_exprs(exprs: &Vec<Expr>) -> Vec<Expr> {
+    find_exprs_in_exprs(exprs, &|nested_expr| match nested_expr {

Review comment:
       Can use `matches!` macro here?




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