[GitHub] [arrow] alamb commented on a change in pull request #9682: ARROW-7364: [Rust][DataFusion] Add cast options to cast kernel and TRY_CAST to DataFusion

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

alamb commented on a change in pull request #9682:
URL: https://github.com/apache/arrow/pull/9682#discussion_r606691319



##########
File path: rust/arrow/src/compute/kernels/cast.rs
##########
@@ -937,114 +1048,169 @@ where
         from.as_any()
             .downcast_ref::<GenericStringArray<Offset>>()
             .unwrap(),
-    )))
+        cast_options,
+    )?))
 }
 
 fn string_to_numeric_cast<T, Offset: StringOffsetSizeTrait>(
     from: &GenericStringArray<Offset>,
-) -> PrimitiveArray<T>
+    cast_options: &CastOptions,
+) -> Result<PrimitiveArray<T>>
 where
     T: ArrowNumericType,
     <T as ArrowPrimitiveType>::Native: lexical_core::FromLexical,
 {
-    let iter = (0..from.len()).map(|i| {
-        if from.is_null(i) {
-            None
-        } else {
-            lexical_core::parse(from.value(i).as_bytes()).ok()
-        }
-    });
+    let vec = (0..from.len())
+        .map(|i| {
+            if from.is_null(i) {
+                Ok(None)
+            } else {
+                let string = from.value(i);
+                let result = lexical_core::parse(string.as_bytes());
+                if cast_options.safe {
+                    Ok(result.ok())
+                } else {
+                    Some(result.map_err(|_| {
+                        ArrowError::CastError(format!(
+                            "Cannot cast string '{}' to value of {} type",
+                            string,
+                            std::any::type_name::<T>()
+                        ))
+                    }))
+                    .transpose()
+                }
+            }
+        })
+        .collect::<Result<Vec<Option<_>>>>()?;

Review comment:
       I wonder if we need the collect here (and the few places below)? It seems like we might be able to use the iter directly for the case where `cast_options.safe == true` 
   
   I worry that unsafe casts may get slower if we always created a vec for them
   




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