[GitHub] [arrow] Dandandan commented on a change in pull request #9014: ARROW-11035: [Rust] Improved performance of casting to utf8

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

Dandandan commented on a change in pull request #9014:
URL: https://github.com/apache/arrow/pull/9014#discussion_r548944938



##########
File path: rust/arrow/src/compute/kernels/cast.rs
##########
@@ -895,31 +886,22 @@ where
     FROM: ArrowNumericType,
     FROM::Native: std::string::ToString,
 {
-    numeric_to_string_cast::<FROM>(
+    Ok(Arc::new(numeric_to_string_cast::<FROM>(
         array
             .as_any()
             .downcast_ref::<PrimitiveArray<FROM>>()
             .unwrap(),
-    )
-    .map(|to| Arc::new(to) as ArrayRef)
+    )))
 }
 
-fn numeric_to_string_cast<T>(from: &PrimitiveArray<T>) -> Result<StringArray>
+fn numeric_to_string_cast<T>(from: &PrimitiveArray<T>) -> StringArray
 where
     T: ArrowPrimitiveType + ArrowNumericType,
     T::Native: std::string::ToString,
 {
-    let mut b = StringBuilder::new(from.len());
-
-    for i in 0..from.len() {
-        if from.is_null(i) {
-            b.append(false)?;
-        } else {
-            b.append_value(&from.value(i).to_string())?;
-        }
-    }
-
-    Ok(b.finish())
+    from.iter()
+        .map(|maybe_value| maybe_value.map(|value| value.to_string()))

Review comment:
       Note, we probably can use lexical like here later https://github.com/apache/arrow/pull/9010




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