feat(cast): support cast between struct

arrow-cast/src/cast.rs

@@ -160,6 +160,12 @@ pub fn can_cast_types(from_type: &DataType, to_type: &DataType) -> bool {
         (Decimal128(_, _) | Decimal256(_, _), Utf8 | LargeUtf8) => true,
         // Utf8 to decimal
         (Utf8 | LargeUtf8, Decimal128(_, _) | Decimal256(_, _)) => true,
+		(Struct(from_fields), Struct(to_fields)) => {
+			from_fields.len() == to_fields.len() &&
+				from_fields.iter().zip(to_fields.iter()).all(|(f1, f2)| {
+					can_cast_types(f1.data_type(), f2.data_type())
+				})
+		}
         (Struct(_), _) => false,
         (_, Struct(_)) => false,
         (_, Boolean) => {
@@ -1138,11 +1144,22 @@ pub fn cast_with_options(
                 ))),
             }
         }
+        (Struct(_), Struct(to_fields)) => {
+            let array = array.as_any().downcast_ref::<StructArray>().unwrap();
+            let fields = array
+                .columns()
+                .iter()
+                .zip(to_fields.iter())
+                .map(|(l, field)| cast_with_options(l, field.data_type(), cast_options))
+                .collect::<Result<Vec<ArrayRef>, ArrowError>>()?;
+            let array = StructArray::new(to_fields.clone(), fields, array.nulls().cloned());
+            Ok(Arc::new(array) as ArrayRef)
+        }
         (Struct(_), _) => Err(ArrowError::CastError(
-            "Cannot cast from struct to other types".to_string(),
+            "Cannot cast from struct to other types except struct".to_string(),
         )),
         (_, Struct(_)) => Err(ArrowError::CastError(
-            "Cannot cast to struct from other types".to_string(),
+            "Cannot cast to struct from other types except struct".to_string(),
         )),
         (_, Boolean) => match from_type {
             UInt8 => cast_numeric_to_bool::<UInt8Type>(array),
@@ -9447,4 +9464,65 @@ mod tests {
             );
         }
     }
+    #[test]
+    fn test_cast_struct_to_struct() {
+        let struct_type = DataType::Struct(
+            vec![
+                Field::new("a", DataType::Boolean, false),
+                Field::new("b", DataType::Int32, false),
+            ]
+            .into(),
+        );
+        let to_type = DataType::Struct(
+            vec![
+                Field::new("a", DataType::Utf8, false),
+                Field::new("b", DataType::Utf8, false),
+            ]
+            .into(),
+        );
+        let boolean = Arc::new(BooleanArray::from(vec![false, false, true, true]));
+        let int = Arc::new(Int32Array::from(vec![42, 28, 19, 31]));
+        let struct_array = StructArray::from(vec![
+            (
+                Arc::new(Field::new("b", DataType::Boolean, false)),
+                boolean.clone() as ArrayRef,
+            ),
+            (
+                Arc::new(Field::new("c", DataType::Int32, false)),
+                int.clone() as ArrayRef,
+            ),
+        ]);
+        let casted_array = cast(&struct_array, &to_type).unwrap();
+        let casted_array = casted_array.as_struct();
+        assert_eq!(casted_array.data_type(), &to_type);
+        let casted_boolean_array = casted_array
+            .column(0)
+            .as_string::<i32>()
+            .into_iter()
+            .flatten()
+            .collect::<Vec<_>>();
+        let casted_int_array = casted_array
+            .column(1)
+            .as_string::<i32>()
+            .into_iter()
+            .flatten()
+            .collect::<Vec<_>>();
+        assert_eq!(casted_boolean_array, vec!["false", "false", "true", "true"]);
+        assert_eq!(casted_int_array, vec!["42", "28", "19", "31"]);
+
+        // test for can't cast
+        let to_type = DataType::Struct(
+            vec![
+                Field::new("a", DataType::Date32, false),
+                Field::new("b", DataType::Utf8, false),
+            ]
+            .into(),
+        );
+        assert!(!can_cast_types(&struct_type, &to_type));
+        let result = cast(&struct_array, &to_type);
+        assert_eq!(
+            "Cast error: Casting from Boolean to Date32 not supported",
+            result.unwrap_err().to_string()
+        );
+    }
 }