feat: Support cast to large list. (#1547)

src/compute/cast/mod.rs

@@ -104,6 +104,7 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
         (List(list_from), LargeList(list_to)) if list_from == list_to => true,
         (LargeList(list_from), List(list_to)) if list_from == list_to => true,
         (_, List(list_to)) => can_cast_types(from_type, &list_to.data_type),
+        (_, LargeList(list_to)) => can_cast_types(from_type, &list_to.data_type),
         (Dictionary(_, from_value_type, _), Dictionary(_, to_value_type, _)) => {
             can_cast_types(from_value_type, to_value_type)
         }
@@ -509,6 +510,19 @@ pub fn cast(array: &dyn Array, to_type: &DataType, options: CastOptions) -> Resu
             Ok(Box::new(list_array))
         }
 
+        (_, LargeList(to)) => {
+            // cast primitive to list's primitive
+            let values = cast(array, &to.data_type, options)?;
+            // create offsets, where if array.len() = 2, we have [0,1,2]
+            let offsets = (0..=array.len() as i64).collect::<Vec<_>>();
+            // Safety: offsets _are_ monotonically increasing
+            let offsets = unsafe { Offsets::new_unchecked(offsets) };
+
+            let list_array = ListArray::<i64>::new(to_type.clone(), offsets.into(), values, None);
+
+            Ok(Box::new(list_array))
+        }
+
         (Dictionary(index_type, ..), _) => match_integer_type!(index_type, |$T| {
             dictionary_cast_dyn::<$T>(array, to_type, options)
         }),

tests/it/compute/cast.rs

@@ -1,5 +1,6 @@
 use arrow2::array::*;
 use arrow2::compute::cast::{can_cast_types, cast, CastOptions};
+use arrow2::datatypes::DataType::LargeList;
 use arrow2::datatypes::*;
 use arrow2::types::{days_ms, months_days_ns, NativeType};
 
@@ -120,6 +121,28 @@ fn i32_to_i32() {
     assert_eq!(c, &expected);
 }
 
+#[test]
+fn i32_to_large_list_i32() {
+    let array = Int32Array::from_slice([5, 6, 7, 8, 9]);
+    let b = cast(
+        &array,
+        &LargeList(Box::new(Field::new("item", DataType::Int32, true))),
+        CastOptions::default(),
+    )
+    .unwrap();
+
+    let arr = b.as_any().downcast_ref::<ListArray<i64>>().unwrap();
+    assert_eq!(&[0, 1, 2, 3, 4, 5], arr.offsets().as_slice());
+    let values = arr.values();
+    let c = values
+        .as_any()
+        .downcast_ref::<PrimitiveArray<i32>>()
+        .unwrap();
+
+    let expected = Int32Array::from_slice([5, 6, 7, 8, 9]);
+    assert_eq!(c, &expected);
+}
+
 #[test]
 fn i32_to_list_i32() {
     let array = Int32Array::from_slice([5, 6, 7, 8, 9]);