[GitHub] [arrow] alamb commented on a change in pull request #8460: ARROW-10236: [Rust] Add can_cast_types to arrow cast kernel, use in DataFusion

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

alamb commented on a change in pull request #8460:
URL: https://github.com/apache/arrow/pull/8460#discussion_r504721964



##########
File path: rust/arrow/src/compute/kernels/cast.rs
##########
@@ -356,11 +520,24 @@ pub fn cast(array: &ArrayRef, to_type: &DataType) -> Result<ArrayRef> {
 
         // temporal casts
         (Int32, Date32(_)) => cast_array_data::<Date32Type>(array, to_type.clone()),
-        (Int32, Time32(_)) => cast_array_data::<Date32Type>(array, to_type.clone()),
+        (Int32, Time32(TimeUnit::Second)) => {

Review comment:
       It is not possible to cast Int32 to a Time32(Microsecond) or Time32(Nanosecond)

##########
File path: rust/arrow/src/compute/kernels/cast.rs
##########
@@ -549,7 +726,18 @@ pub fn cast(array: &ArrayRef, to_type: &DataType) -> Result<ArrayRef> {
         (Timestamp(from_unit, _), Date64(_)) => {
             let from_size = time_unit_multiple(&from_unit);
             let to_size = MILLISECONDS;
-            if from_size != to_size {
+
+            // Scale time_array by (to_size / from_size) using a

Review comment:
       Without this code, casting from a timestamp 32 -> Date64 would result in a divide by zero error (as `from_size / to_size` was `1 / 1000 == 0`

##########
File path: rust/arrow/src/datatypes.rs
##########
@@ -1129,6 +1129,16 @@ impl DataType {
             DataType::Dictionary(_, _) => json!({ "name": "dictionary"}),
         }
     }
+
+    /// Returns true if this type is numeric: (UInt*, Unit*, or Float*)
+    pub fn is_numeric(t: &DataType) -> bool {

Review comment:
       As suggested by @nevi-me on https://github.com/apache/arrow/pull/8400#discussion_r501851945




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