C# List 根据对象属性去重的四种方法对比

原文：https://www.cnblogs.com/s0611163/archive/2019/08/23/11399898.html

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

";
            textBox1.Text += "使用方法一去重耗时：" + d1 + "毫秒

";
            textBox1.Text += "使用ToLookup和ToDictionary去重耗时：" + d2 + "毫秒

";
            textBox1.Text += "使用Distinct去重耗时：" + d3 + "毫秒

";
            textBox1.Text += "使用GroupBy和Select去重耗时：" + d4 + "毫秒

";
            textBox1.Text += "去重后数量：" + r1.Count + "，" + result2.Count + "，" + result3.Count + "，" + result4.Count + "" + "

";
        }));
    });
}

数据类：

public class MyData
{
    public string id { get; set; }
    public string name { get; set; }
}

public class MyCompare : IEqualityComparer<MyData>
{
    public bool Equals(MyData x, MyData y)
    {
        return x.name == y.name;
    }

    public int GetHashCode(MyData obj)
    {
        return obj.name.GetHashCode();
    }
}

测试结果：

结论：

方法一和方法三去重速度差不多，在一个数量级

方法二和方法四去重速度差不多，在一个数量级

方法二和方法四比方法一和方法三大约慢4、5倍左右

方法二和方法四比较方便，一行代码搞定，方法一和方法三代码行数相对较多，方法三要写个MyCompare