fix: fix UniqueBy bug

README.md

@@ -1416,7 +1416,7 @@ import "github.com/duke-git/lancet/v2/slice"
 -   **<big>Unique</big>** : remove duplicate elements in slice.
     [[doc](https://github.com/duke-git/lancet/blob/main/docs/en/api/packages/slice.md#Unique)]
     [[play](https://go.dev/play/p/AXw0R3ZTE6a)]
--   **<big>UniqueBy</big>** : call iteratee func with every item of slice, then remove duplicated.
+-   **<big>UniqueBy</big>** : remove duplicate elements from the input slice based on the values returned by the iteratee function.
     [[doc](https://github.com/duke-git/lancet/blob/main/docs/en/api/packages/slice.md#UniqueBy)]
     [[play](https://go.dev/play/p/UR323iZLDpv)]
 -   **<big>UniqueByField</big>** : remove duplicate elements in struct slice by struct field.

README_zh-CN.md

@@ -1417,7 +1417,7 @@ import "github.com/duke-git/lancet/v2/slice"
 -   **<big>Unique</big>** : 删除切片中的重复元素。
     [[doc](https://github.com/duke-git/lancet/blob/main/docs/api/packages/slice.md#Unique)]
     [[play](https://go.dev/play/p/AXw0R3ZTE6a)]
--   **<big>UniqueBy</big>** : 对切片的每个元素调用 iteratee 函数，然后删除重复元素。
+-   **<big>UniqueBy</big>** : 根据迭代函数返回的值，从输入切片中移除重复元素。此函数保持元素的顺序。
     [[doc](https://github.com/duke-git/lancet/blob/main/docs/api/packages/slice.md#UniqueBy)]
     [[play](https://go.dev/play/p/UR323iZLDpv)]
 -   **<big>UniqueByField</big>** : 根据struct字段对struct切片去重复。

docs/api/packages/slice.md

@@ -2284,12 +2284,12 @@ func main() {
 
 ### <span id="UniqueBy">UniqueBy</span>
 
-<p>对切片的每个元素调用iteratee函数，然后删除重复元素</p>
+<p>根据迭代函数返回的值，从输入切片中移除重复元素。此函数保持元素的顺序。</p>
 
 <b>函数签名:</b>
 
 ```go
-func UniqueBy[T comparable](slice []T, iteratee func(item T) T) []T
+func UniqueBy[T any, U comparable](slice []T, iteratee func(item T) U) []T
 ```
 
 <b>示例:<span style="float:right;display:inline-block;">[运行](https://go.dev/play/p/UR323iZLDpv)</span></b>
@@ -2309,7 +2309,7 @@ func main() {
     fmt.Println(result)
 
     // Output:
-    // [1 2 0]
+    // [1 2 3]
 }
 ```
 

docs/en/api/packages/slice.md

@@ -2282,12 +2282,12 @@ func main() {
 
 ### <span id="UniqueBy">UniqueBy</span>
 
-<p>Call iteratee func with every item of slice, then remove duplicated.</p>
+<p>Removes duplicate elements from the input slice based on the values returned by the iteratee function. this function maintains the order of the elements.</p>
 
 <b>Signature:</b>
 
 ```go
-func UniqueBy[T comparable](slice []T, iteratee func(item T) T) []T
+func UniqueBy[T any, U comparable](slice []T, iteratee func(item T) U) []T
 ```
 
 <b>Example:<span style="float:right;display:inline-block;">[Run](https://go.dev/play/p/UR323iZLDpv)</span></b>
@@ -2307,7 +2307,7 @@ func main() {
     fmt.Println(result)
 
     // Output:
-    // [1 2 0]
+    // [1 2 3]
 }
 ```
 

slice/slice.go

@@ -783,17 +783,25 @@ func Unique[T comparable](slice []T) []T {
 	return result
 }
 
-// UniqueBy call iteratee func with every item of slice, then remove duplicated.
-// Play: https://go.dev/play/p/UR323iZLDpv
-func UniqueBy[T comparable](slice []T, iteratee func(item T) T) []T {
-	result := []T{}
+// UniqueBy removes duplicate elements from the input slice based on the values returned by the iteratee function.
+// The function maintains the order of the elements.
+// Play: todo
+func UniqueBy[T any, U comparable](slice []T, iteratee func(item T) U) []T {
+	result := make([]T, 0, len(slice))
+	seen := make(map[U]struct{}, len(slice))
 
-	for _, v := range slice {
-		val := iteratee(v)
-		result = append(result, val)
+	for i := range slice {
+		key := iteratee(slice[i])
+		if _, ok := seen[key]; ok {
+			continue
+		}
+
+		seen[key] = struct{}{}
+
+		result = append(result, slice[i])
 	}
 
-	return Unique(result)
+	return result
 }
 
 // UniqueByField remove duplicate elements in struct slice by struct field.

slice/slice_example_test.go

@@ -777,7 +777,7 @@ func ExampleUniqueBy() {
 	fmt.Println(result)
 
 	// Output:
-	// [1 2 0]
+	// [1 2 3]
 }
 
 func ExampleUniqueByField() {

slice/slice_test.go

@@ -733,7 +733,8 @@ func TestUniqueBy(t *testing.T) {
 	actual := UniqueBy([]int{1, 2, 3, 4, 5, 6}, func(val int) int {
 		return val % 4
 	})
-	assert.Equal([]int{1, 2, 3, 0}, actual)
+
+	assert.Equal([]int{1, 2, 3, 4}, actual)
 }
 
 func TestUniqueByField(t *testing.T) {