C# List 去重的三種方法

三種去重的方法

1、List中的元素實現IEquatabe接口，並提供Equals方法和GetHashCode方法。

2、使用表達式

users.Where((x,i)=>users.FindIndex(z=>z.name == x.name) == i)

 3、使用循環，判斷每個元素是否重復

    using System;  
    using System.Collections.Generic;  
    using System.Linq;  
      
    namespace NonDuplicateList  
    {  
        class Program  
        {  
            static void Main(string[] args)  
            {  
                List<User> users = new List<User>();  
                users.Add(new User("張三", "永豐路299號"));  
                users.Add(new User("張三", "上地西路8號"));//重復項，去重后將刪掉  
                users.Add(new User("李四", "海鷹路甲一號"));  
      
                List<User> nonDuplicateList1 = users.Distinct().ToList();//通過User類的Equals實現去重  
                List<User> nonDuplicateList2 = users.Where((x,i)=>users.FindIndex(z=>z.name == x.name) == i).ToList();//Lambda表達式去重  
                List<User> nonDuplicateList3 = new List<User>();//通過循環方式去重  
                foreach(User user in users)  
                {  
                    if(nonDuplicateList3.Exists(x=>x.name==user.name) == false)  
                    {  
                        nonDuplicateList3.Add(user);  
                    }  
                }  
      
                foreach(List<User> list in new Object[]{nonDuplicateList1,nonDuplicateList2,nonDuplicateList3})//打印出三個List的元素  
                {  
                    Console.Write("nonDuplicateList:\r\n");  
                    foreach(User u in list)  
                    {  
                        Console.WriteLine("\t" + u.ToString());  
                    }  
                }  
                Console.Read();  
            }  
        }  
      
        class User:IEquatable<User>//繼承IEquatable接口，實現Equals方法。List就可以使用Distinct去重  
        {  
            public string name { get; set; }  
            string address;  
      
            public User(string _name, string _address)  
            {  
                name = _name;  
                address = _address;  
            }  
      
            public override string ToString()  
            {  
                return string.Format("name:{0},\taddress:{1}", name, address);  
            }  
      
            public bool Equals(User other)  
            {  
                return this.name == other.name;  
            }  
            public override int GetHashCode()  
            {  
                return name.GetHashCode();  
            }  
        }  
    }