feat: add ReduceRight

slice/slice.go

@@ -504,6 +504,18 @@ func ReduceBy[T any, U any](slice []T, initial U, reducer func(index int, item T
 	return accumulator
 }
 
+// ReduceRight is like ReduceBy, but it iterates over elements of slice from right to left.
+// Play: todo
+func ReduceRight[T any, U any](slice []T, initial U, reducer func(index int, item T, agg U) U) U {
+	accumulator := initial
+
+	for i := len(slice) - 1; i >= 0; i-- {
+		accumulator = reducer(i, slice[i], accumulator)
+	}
+
+	return accumulator
+}
+
 // Replace returns a copy of the slice with the first n non-overlapping instances of old replaced by new.
 // Play: https://go.dev/play/p/P5mZp7IhOFo
 func Replace[T comparable](slice []T, old T, new T, n int) []T {

slice/slice_example_test.go

@@ -477,6 +477,17 @@ func ExampleReduceBy() {
 	// 1234
 }
 
+func ExampleReduceRight() {
+	result := ReduceRight([]int{1, 2, 3, 4}, "", func(_ int, item int, agg string) string {
+		return agg + fmt.Sprintf("%v", item)
+	})
+
+	fmt.Println(result)
+
+	// Output:
+	// 4321
+}
+
 func ExampleReplace() {
 	strs := []string{"a", "b", "c", "a"}
 

slice/slice_test.go

@@ -406,7 +406,7 @@ func TestReduce(t *testing.T) {
 }
 
 func TestReduceBy(t *testing.T) {
-	assert := internal.NewAssert(t, "TestReduce2")
+	assert := internal.NewAssert(t, "TestReduceBy")
 
 	result1 := ReduceBy([]int{1, 2, 3, 4}, 0, func(_ int, item int, agg int) int {
 		return agg + item
@@ -421,6 +421,16 @@ func TestReduceBy(t *testing.T) {
 
 }
 
+func TestReduceRight(t *testing.T) {
+	assert := internal.NewAssert(t, "ReduceRight")
+
+	result := ReduceRight([]int{1, 2, 3, 4}, "", func(_ int, item int, agg string) string {
+		return agg + fmt.Sprintf("%v", item)
+	})
+
+	assert.Equal("4321", result)
+}
+
 func TestIntSlice(t *testing.T) {
 	var nums []any
 	nums = append(nums, 1, 2, 3)