diff --git a/package.json b/package.json
index 3ae4a99..2eb0370 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "web-utility",
-    "version": "4.7.0",
+    "version": "4.7.1",
     "license": "LGPL-3.0",
     "author": "shiy2008@gmail.com",
     "description": "Web front-end toolkit based on TypeScript",
diff --git a/source/data.ts b/source/data.ts
index 0733cee..32ebad5 100644
--- a/source/data.ts
+++ b/source/data.ts
@@ -134,14 +134,13 @@ export enum DiffStatus {
 }
 
 export function diffKeys<T extends IndexKey>(oldList: T[], newList: T[]) {
+    const oldSet = new Set(oldList),
+        newSet = new Set(newList);
     const map = {} as Record<T, DiffStatus>;
 
-    for (const item of oldList) map[item] = DiffStatus.Old;
-
-    for (const item of newList) {
-        map[item] ||= 0;
-        map[item] += DiffStatus.New;
-    }
+    for (const item of oldSet.difference(newSet)) map[item] = DiffStatus.Old;
+    for (const item of oldSet.intersection(newSet)) map[item] = DiffStatus.Same;
+    for (const item of newSet.difference(oldSet)) map[item] = DiffStatus.New;
 
     return {
         map,
diff --git a/test/data.spec.ts b/test/data.spec.ts
index 819a7af..7a7d2bd 100644
--- a/test/data.spec.ts
+++ b/test/data.spec.ts
@@ -153,6 +153,17 @@ describe('Data', () => {
         });
     });
 
+    it('should ignore duplicate keys when comparing key arrays', () => {
+        expect(diffKeys(['a', 'a', 'b'], ['b', 'b', 'c', 'c'])).toEqual({
+            map: { a: DiffStatus.Old, b: DiffStatus.Same, c: DiffStatus.New },
+            group: {
+                [DiffStatus.Old]: [['a', DiffStatus.Old]],
+                [DiffStatus.Same]: [['b', DiffStatus.Same]],
+                [DiffStatus.New]: [['c', DiffStatus.New]]
+            }
+        });
+    });
+
     it('should detect an Object whether is Array-like or not', () => {
         expect(likeArray(NaN)).toBe(false);
         expect(likeArray('a')).toBe(true);