support distinct

README.md

@@ -4,6 +4,7 @@
 gollection is golang collection util library (inspired by [kotlin collection](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/index.html))
 
 # supported functions
+- distinct
 - filter
 - flatMap
 - flatten

distinct.go

@@ -14,7 +14,7 @@ func (g *gollection) Distinct() *gollection {
 	if sv.Kind() != reflect.Slice {
 		return &gollection{
 			slice: nil,
-			err:   fmt.Errorf("gollection.Take called with non-slice value of type %T", g.slice),
+			err:   fmt.Errorf("gollection.Distinct called with non-slice value of type %T", g.slice),
 		}
 	}
 
@@ -33,3 +33,33 @@ func (g *gollection) Distinct() *gollection {
 		slice: ret.Interface(),
 	}
 }
+
+func (g *gollection) DistinctBy(f func(v interface{}) interface{}) *gollection {
+	if g.err != nil {
+		return &gollection{err: g.err}
+	}
+
+	sv := reflect.ValueOf(g.slice)
+	if sv.Kind() != reflect.Slice {
+		return &gollection{
+			slice: nil,
+			err:   fmt.Errorf("gollection.DistinctBy called with non-slice value of type %T", g.slice),
+		}
+	}
+
+	ret := reflect.MakeSlice(sv.Type(), 0, sv.Len())
+	m := make(map[interface{}]bool)
+
+	for i := 0; i < sv.Len(); i++ {
+		v := sv.Index(i)
+		id := f(v.Interface())
+		if _, ok := m[id]; !ok {
+			ret = reflect.Append(ret, v)
+			m[id] = true
+		}
+	}
+
+	return &gollection{
+		slice: ret.Interface(),
+	}
+}

distinct_test.go

@@ -28,3 +28,31 @@ func TestDistinct_HavingError(t *testing.T) {
 	_, err := gollection.New("not slice value").Distinct().Distinct().Result()
 	assert.Error(err)
 }
+
+func TestDistinctBy(t *testing.T) {
+	assert := assert.New(t)
+	arr := []string{"aaa", "bb", "c", "ddd", "ee", "f"}
+	expect := []string{"aaa", "bb", "c"}
+
+	res, err := gollection.New(arr).DistinctBy(func(v interface{}) interface{} {
+		return len(v.(string))
+	}).Result()
+	assert.NoError(err)
+	assert.Equal(expect, res)
+}
+
+func TestDistinctBy_NotSlice(t *testing.T) {
+	assert := assert.New(t)
+	_, err := gollection.New("not slice value").DistinctBy(func(v interface{}) interface{} {
+		return v
+	}).Result()
+	assert.Error(err)
+}
+
+func TestDistinctBy_HavingError(t *testing.T) {
+	assert := assert.New(t)
+	_, err := gollection.New("not slice value").DistinctBy(func(v interface{}) interface{} {
+		return v
+	}).Distinct().Result()
+	assert.Error(err)
+}

examples/distinct/main.go

@@ -12,4 +12,23 @@ func main() {
 	res, _ := gollection.New(arr).Distinct().Result()
 	fmt.Println("origin : ", arr)
 	fmt.Println("ret    : ", res) // {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
+
+	type user struct {
+		ID   int64
+		Name string
+	}
+	users := []user{
+		{ID: 1, Name: "Ann"},
+		{ID: 2, Name: "Bob"},
+		{ID: 3, Name: "Charles"},
+		{ID: 4, Name: "Ann"},
+		{ID: 5, Name: "Bob"},
+		{ID: 6, Name: "Charles"},
+	}
+
+	res, _ = gollection.New(users).DistinctBy(func(v interface{}) interface{} {
+		return v.(user).Name
+	}).Result()
+	fmt.Println("origin : ", users)
+	fmt.Println("ret    : ", res)
 }