[GitHub] [arrow-datafusion] jychen7 commented on a change in pull request #519: 110 support group by positions

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

jychen7 commented on a change in pull request #519:
URL: https://github.com/apache/arrow-datafusion/pull/519#discussion_r646195188



##########
File path: datafusion/src/sql/utils.rs
##########
@@ -390,6 +390,42 @@ pub(crate) fn extract_aliases(exprs: &[Expr]) -> HashMap<String, Expr> {
         .collect::<HashMap<String, Expr>>()
 }
 
+/// Returns mapping of each position (`String`) to the expression (`Expr`) it is
+/// aliasing.
+pub(crate) fn extract_positions(exprs: &[Expr]) -> HashMap<String, Expr> {
+    let mut position = 0;
+    exprs
+        .iter()
+        .filter_map(|expr| match expr {
+            // position starts with 1
+            Expr::Alias(nested_expr, _alias_name) => {
+                position += 1;
+                Some((position.clone().to_string(), *nested_expr.clone()))
+            }
+            _ => {
+                position += 1;
+                Some((position.clone().to_string(), expr.clone()))
+            }
+        })
+        .collect::<HashMap<String, Expr>>()
+}
+
+pub(crate) fn resolve_positions_to_exprs(
+    expr: &Expr,
+    positions: &HashMap<String, Expr>,
+) -> Result<Expr> {

Review comment:
       @Dandandan thanks for the suggestion.
   I use HashMap initially because of the `to_string()` type cast is easier to handle. After some exploring, I now change it to array.




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