Biegral Blog

在List中，Contains, Exists, Any都可以实现判断元素是否存在。

先上结果。性能方面：Contains 优于 Exists 优于 Any

以下为测试代码

public static void Contains_Exists_Any_Test(int num)
        {
            List<int> list = new List<int>();

            int N = num;
            for (int i = 0; i < N; i++)
            {
                list.Add(i);
            }
            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            sw.Start();
            Console.WriteLine(list.Contains(N));
            sw.Stop();
            Console.WriteLine("Contains:"+sw.Elapsed.ToString());

            sw.Start();
            Console.WriteLine(list.Exists(i => i == N));
            sw.Stop();
            Console.WriteLine("Exists:"+ sw.Elapsed.ToString());

            sw.Start();
            Console.WriteLine(list.Any(i => i == N));
            sw.Stop();
            Console.WriteLine("Any:"+ sw.Elapsed.ToString());
        }

在开发过程中可以根据实际情况进行选择，当list中数据量不大时使用Exists代码更简洁易懂；数据量大时推荐使用Contains；不推荐使用Any。

下面的代码对比就能看出为啥数据量不大的时候推荐Exists了。

class ITEM_GIDComparer : IEqualityComparer<T>
    {
        public bool Equals(T orl1, T orl2)
         {
             if (orl1==null)
             {
                 return orl2 == null;
             }
             return orl1.ITEM_GID == orl2.ITEM_GID;
         }

        public int GetHashCode(T orl)
         {
             if (orl == null)
                 return 0;
             return orl.ITEM_GID.GetHashCode();
         } 
    }
    orlclst.Contains(orlc, new ITEM_GIDComparer())
    //Exists一行代码就可以实现上面的功能
    orlclst.Exists(x=>x.ITEM_GID==orlc.ITEM_GID)

C#比较两个list集合，两集合同时存在或A集合存在B集合中无

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Test
{
    class Program 
    {
        static void Main(string[] args)
        {
            var student1 = new List<student>();
            student1.Add(new student() { name = "张三", subject = "英语", score = 89 });
            student1.Add(new student() { name = "李四", subject = "英语", score = 95 });
            student1.Add(new student() { name = "王五", subject = "英语", score = 69 });
            student1.Add(new student() { name = "李倩", subject = "英语", score = 99 });

            var student2 = new List<student>();
            student2.Add(new student() { name = "李四", subject = "英语", score = 95 });
            student2.Add(new student() { name = "王五", subject = "数学", score = 69 });
            student2.Add(new student() { name = "赵六", subject = "数学", score = 100 });

            //var exp1 = student1.Where(a => student2.Any(t => a.name.Contains(t.name))).ToList();  
            //使用Exists同样可以实现 字面上应该更好理解，而且效率要高些  
            var exp1 = student1.Where(a => student2.Exists(t => a.name.Contains(t.name))).ToList();
            Console.WriteLine("--查找student1和student2总同时存在的数据--");
            foreach (var item in exp1)
            {
                Console.WriteLine("{0} \t {1} \t {2}", item.name, item.subject, item.score);
            }

            //var exp2 = student1.Where(a => student2.All(t => !a.name.Contains(t.name))).ToList();    
            //使用Exists同样可以实现 字面上应该更好理解，而且效率要高些  
            var exp2 = student1.Where(a => !student2.Exists(t => a.name.Contains(t.name))).ToList();
            Console.WriteLine("--查找student1集合中存在，而student2不存在的数据--");
            foreach (var item in exp2)
            {
                Console.WriteLine("{0} \t {1} \t {2}", item.name, item.subject, item.score);
            }

            var exp3 = student2.Where(a => !student1.Exists(t => a.name.Contains(t.name))).ToList();
            Console.WriteLine("--查找student2集合中存在，而student1不存在的数据--");
            foreach (var item in exp3)
            {
                Console.WriteLine("{0} \t {1} \t {2}", item.name, item.subject, item.score);
            }
            Console.Read();   

        }

        public class student
        {
            /// <summary>    
            /// 姓名    
            /// </summary>    
            public string name;
            /// <summary>    
            /// 科目    
            /// </summary>    
            public string subject;
            /// <summary>    
            /// 分数    
            /// </summary>    
            public int score;
        }

    }

}

运行结果如图: