[GitHub] [arrow-datafusion] Dandandan commented on a change in pull request #2128: MINOR: fix concat_ws corner bug

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

Dandandan commented on a change in pull request #2128:
URL: https://github.com/apache/arrow-datafusion/pull/2128#discussion_r840891530



##########
File path: datafusion/physical-expr/src/string_expressions.rs
##########
@@ -343,18 +343,17 @@ pub fn concat_ws(args: &[ArrayRef]) -> Result<ArrayRef> {
         .enumerate()
         .map(|(index, x)| {
             x.map(|sep: &str| {
-                let mut owned_string: String = "".to_owned();
-                for arg_index in 1..args.len() {
-                    let arg = &args[arg_index];
-                    if !arg.is_null(index) {
-                        owned_string.push_str(arg.value(index));
-                        // if not last push separator
-                        if arg_index != args.len() - 1 {
-                            owned_string.push_str(sep);
+                let string_vec = args[1..]
+                    .iter()
+                    .flat_map(|arg| {
+                        if !arg.is_null(index) {
+                            vec![arg.value(index)]
+                        } else {
+                            vec![]

Review comment:
       ```suggestion
                           if !arg.is_null(index) {
                               Some(arg.value(index))
                           } else {
                               None
                           }
   ```
   




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