[GitHub] [arrow-rs] metesynnada commented on a diff in pull request #4020: feat: cast from/to interval and duration

["metesynnada (via GitHub)" <gi...@apache.org>]

metesynnada commented on code in PR #4020:
URL: https://github.com/apache/arrow-rs/pull/4020#discussion_r1161265013


##########
arrow-cast/src/cast.rs:
##########
@@ -458,6 +460,93 @@ where
     }
 }
 
+/// Cast the array from interval to duration
+fn cast_interval_to_duration<D: ArrowTemporalType<Native = i64>>(
+    array: &dyn Array,
+    cast_options: &CastOptions,
+) -> Result<ArrayRef, ArrowError> {
+    let array = array
+        .as_any()
+        .downcast_ref::<IntervalMonthDayNanoArray>()
+        .unwrap();
+
+    let mut builder = PrimitiveBuilder::<D>::new();
+
+    let scale = match D::DATA_TYPE {
+        DataType::Duration(TimeUnit::Second) => 1_000_000_000,
+        DataType::Duration(TimeUnit::Millisecond) => 1_000_000,
+        DataType::Duration(TimeUnit::Microsecond) => 1_000,
+        DataType::Duration(TimeUnit::Nanosecond) => 1,
+        _ => unreachable!(),
+    };
+
+    for i in 0..array.len() {
+        if array.is_null(i) {
+            builder.append_null();
+        } else {
+            let v = array.value(i) / scale;
+            if v > i64::MAX as i128 {
+                if cast_options.safe {
+                    builder.append_null();
+                } else {
+                    return Err(ArrowError::ComputeError(format!(
+                        "Cannot cast to {:?}. Overflowing on {:?}",
+                        D::DATA_TYPE,
+                        v
+                    )));
+                }
+            } else {
+                builder.append_value(v as i64);
+            }
+        }
+    }
+
+    Ok(Arc::new(builder.finish()) as ArrayRef)
+}
+
+/// Cast the array from duration and interval
+fn cast_duration_to_interval<D: ArrowTemporalType<Native = i64>>(
+    array: &dyn Array,
+    cast_options: &CastOptions,
+) -> Result<ArrayRef, ArrowError> {
+    let array = array.as_any().downcast_ref::<PrimitiveArray<D>>().unwrap();
+
+    let mut builder = IntervalMonthDayNanoBuilder::new();
+
+    let scale = match array.data_type() {
+        DataType::Duration(TimeUnit::Second) => 1_000_000_000,
+        DataType::Duration(TimeUnit::Millisecond) => 1_000_000,
+        DataType::Duration(TimeUnit::Microsecond) => 1_000,
+        DataType::Duration(TimeUnit::Nanosecond) => 1,
+        _ => unreachable!(),
+    };
+
+    for i in 0..array.len() {
+        if array.is_null(i) {
+            builder.append_null();
+        } else {

Review Comment:
   `PrimitiveArray::from_trusted_len_iter` may fit here.



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