测试代码：
private void TestDistinct() { Task.Run(() => { //生成测试数据 DateTime dt = DateTime.Now; Random rnd = new Random(); List<MyData> list = new List<MyData>(); int total = 1000000; for (int i = 0; i < total; i++) { MyData info = new MyData(); info.id = rnd.Next(1, total * 10).ToString(); info.name = rnd.Next(1, total * 10).ToString(); list.Add(info); } double d = DateTime.Now.Subtract(dt).TotalMilliseconds; //方法一 DateTime dt1 = DateTime.Now; Dictionary<string, MyData> result1 = new Dictionary<string, MyData>(); foreach (MyData item in list) { MyData temp; if (!result1.TryGetValue(item.name, out temp)) { result1.Add(item.name, item); } } List<MyData> r1 = result1.Values.ToList(); double d1 = DateTime.Now.Subtract(dt1).TotalMilliseconds; //方法二 DateTime dt2 = DateTime.Now; List<MyData> result2 = list.ToLookup(item => item.name).ToDictionary(item => item.Key, item => item.First()).Values.ToList(); double d2 = DateTime.Now.Subtract(dt2).TotalMilliseconds; //方法三 DateTime dt3 = DateTime.Now; List<MyData> result3 = list.Distinct(new MyCompare()).ToList(); double d3 = DateTime.Now.Subtract(dt3).TotalMilliseconds; //方法四 DateTime dt4 = DateTime.Now; List<MyData> result4 = list.GroupBy(item => item.name).Select(item => item.First()).ToList(); double d4 = DateTime.Now.Subtract(dt4).TotalMilliseconds; this.BeginInvoke(new Action(() => { textBox1.Text = ""; textBox1.Text += "生成 " + list.Count.ToString("# ####") + " 条测试数据耗时：" + d + "毫秒\r\n\r\n"; textBox1.Text += "使用方法一去重耗时：" + d1 + "毫秒\r\n\r\n"; textBox1.Text += "使用ToLookup和ToDictionary去重耗时：" + d2 + "毫秒\r\n\r\n"; textBox1.Text += "使用Distinct去重耗时：" + d3 + "毫秒\r\n\r\n"; textBox1.Text += "使用GroupBy和Select去重耗时：" + d4 + "毫秒\r\n\r\n"; textBox1.Text += "去重后数量：" + r1.Count + "，" + result2.Count + "，" + result3.Count + "，" + result4.Count + "" + "\r\n\r\n"; })); }); }