c# lambda distinct

最新推荐文章于 2025-05-26 11:07:14 发布

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最新推荐文章于 2025-05-26 11:07:14 发布

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CC 4.0 BY-SA版权

文章标签： c#

原文链接：http://www.cnblogs.com/zwgblogs/p/4743874.html

本文讨论了编程中去重问题的多种解决方法，包括使用Lambda表达式的distinct方法和自定义比较类，适用于简单类型和对象类型的列表。通过对比不同方法的执行效率和简洁性，展示了如何在实际编程中高效地进行数据去重。

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在写程序的时候会遇见这样的问题，那就是去重，有什么方法更快呢。
当去重时，首先想到的是自己写代码，代码大概如下：

   private static void distinctListIntTest()
        {
            Console.WriteLine("未去重");
            List<int> list = new List<int>() { 1, 2, 3, 4, 1, 2, 3, 4 };
            foreach (int inst in list)
            {
                Console.WriteLine(inst);
            }
            Console.WriteLine("=======================");
            Console.WriteLine("去重后");
            List<int> list1 = new List<int>();
            foreach (int inst in list)
            {
                if (!list1.Contains(inst))
                {
                    list1.Add(inst);
                }
            }
            foreach (int inst in list1)
            {
                Console.WriteLine(inst);
            }
        }

这段代码确实能实现我们想要的效果，结果如下：

这段代码虽然能实现，但是要写很多代码，用起来不方便。有没有更好的办法呢，办法是有的，那就是lambda表达式的distinct方法，代码如下：

 private static void distinctListInt()
        {
            Console.WriteLine("未去重");
            List<int> list = new List<int>() { 1, 2, 3, 5, 1, 2, 3, 5 };
            foreach (int inst in list)
            {
                Console.WriteLine(inst);
            }
            Console.WriteLine("=======================");
            Console.WriteLine("去重后");
            list = list.Distinct().ToList();
            foreach (int inst in list)
            {
                Console.WriteLine(inst);
            }
        }

执行结果如下：

当简单的类型可以了，那如果是一个对象怎么办，用自己写的方法代码如下：
首先声明一个对象

public class user
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }

去重的方法

  private static void distinctListEntityTest()
        {
            Console.WriteLine("未去重");
            List<user> list = new List<user>();
            user user = new user() { Name = "张三", Age = 13 };
            list.Add(user);
            user = new user() { Name = "张三", Age = 13 };
            list.Add(user);
            user = new user() { Name = "李四", Age = 14 };
            list.Add(user);
            user = new user() { Name = "李四", Age = 14 };
            list.Add(user);
            user = new user() { Name = "王五", Age = 15 };
            list.Add(user);
            user = new user() { Name = "王五", Age = 15 };
            list.Add(user);
            foreach (user inst in list)
            {
                Console.WriteLine(inst.Name);
            }
            Console.WriteLine("=======================");
            Console.WriteLine("去重后");
            List<user> list1 = new List<user>();
            foreach (user inst in list)
            {
                bool isbool = true;
                foreach (user inst1 in list1)
                {
                    if (inst1.Name.Equals(inst.Name))
                    {
                        isbool = false;
                        break;
                    }
                }
                if (isbool)
                {
                    list1.Add(inst);
                }

            }
            foreach (user inst in list1)
            {
                Console.WriteLine(inst.Name);
            }
        }

去重的方法【lambda表达式】

  private static void distinctListEntityTest()
        {
            Console.WriteLine("未去重");
            List<user> list = new List<user>();
            user user = new user() { Name = "张三", Age = 13 };
            list.Add(user);
            user = new user() { Name = "张三", Age = 13 };
            list.Add(user);
            user = new user() { Name = "李四", Age = 14 };
            list.Add(user);
            user = new user() { Name = "李四", Age = 14 };
            list.Add(user);
            user = new user() { Name = "王五", Age = 15 };
            list.Add(user);
            user = new user() { Name = "王五", Age = 15 };
            list.Add(user);
            foreach (user inst in list)
            {
                Console.WriteLine(inst.Name);
            }
            Console.WriteLine("=======================");
            Console.WriteLine("去重后");
            List<user> list1=new List<user>();
            foreach (user inst in list)
            {
                if (list1.Count(u => u.Name.Equals(inst.Name))>0)//这句用了lambda表达式
                {
                    continue;
                }
                list1.Add(inst);
            }

            foreach (user inst in list1)
            {
                Console.WriteLine(inst.Name);
            }
        }

这两种方法执行结果如下：

下面就用lambda表达式的distinct()方法代码如下

    private static void distinctListEntity()
        {
            Console.WriteLine("未去重");
            List<user> list = new List<user>();
            user user = new user() { Name = "张三", Age = 13 };
            list.Add(user);
            user = new user() { Name = "张三", Age = 13 };
            list.Add(user);
            user = new user() { Name = "李四", Age = 14 };
            list.Add(user);
            user = new user() { Name = "李四", Age = 14 };
            list.Add(user);
            user = new user() { Name = "王五", Age = 15 };
            list.Add(user);
            user = new user() { Name = "王五", Age = 15 };
            list.Add(user);
            foreach (user inst in list)
            {
                Console.WriteLine(inst.Name);
            }
            Console.WriteLine("=======================");
            Console.WriteLine("去重后");

            list = list.Distinct(new userCompare()).ToList();
            foreach (user inst in list)
            {
                Console.WriteLine(inst.Name);
            }
        }
    }

    class userCompare : IEqualityComparer<user>
    {

        #region IEqualityComparer<user> Members

        public bool Equals(user x, user y)
        {

            return x.Name.Equals(y.Name);

        }

        public int GetHashCode(user obj)
        {

            return obj.Name.GetHashCode();

        }

        #endregion

    }

运行结果如下：