feat: add FlatMap

slice/slice.go

@@ -438,6 +438,18 @@ func FilterMap[T any, U any](slice []T, iteratee func(index int, item T) (U, boo
 	return result
 }
 
+// FlatMap manipulates a slice and transforms and flattens it to a slice of another type.
+// Play: todo
+func FlatMap[T any, U any](slice []T, iteratee func(index int, item T) []U) []U {
+	result := make([]U, 0, len(slice))
+
+	for i, v := range slice {
+		result = append(result, iteratee(i, v)...)
+	}
+
+	return result
+}
+
 // Reduce creates an slice of values by running each element of slice thru iteratee function.
 // Play: https://go.dev/play/p/_RfXJJWIsIm
 func Reduce[T any](slice []T, iteratee func(index int, item1, item2 T) T, initial T) T {

slice/slice_example_test.go

@@ -386,6 +386,20 @@ func ExampleFilterMap() {
 	// []string{"2", "4"}
 }
 
+func ExampleFlatMap() {
+	nums := []int{1, 2, 3, 4}
+
+	result := FlatMap(nums, func(i int, num int) []string {
+		s := "hi-" + strconv.FormatInt(int64(num), 10)
+		return []string{s}
+	})
+
+	fmt.Printf("%#v", result)
+
+	// Output:
+	// []string{"hi-1", "hi-2", "hi-3", "hi-4"}
+}
+
 func ExampleReduce() {
 	nums := []int{1, 2, 3}
 

slice/slice_test.go

@@ -333,6 +333,19 @@ func TestFilterMap(t *testing.T) {
 	assert.Equal([]string{"2", "4"}, result)
 }
 
+func TestFlatMap(t *testing.T) {
+	assert := internal.NewAssert(t, "TestFlatMap")
+
+	nums := []int{1, 2, 3, 4}
+
+	result := FlatMap(nums, func(i int, num int) []string {
+		s := "hi-" + strconv.FormatInt(int64(num), 10)
+		return []string{s}
+	})
+
+	assert.Equal([]string{"hi-1", "hi-2", "hi-3", "hi-4"}, result)
+}
+
 func TestReduce(t *testing.T) {
 	cases := [][]int{
 		{},