LINQ vs foreach vs性能测试结果 [英] LINQ vs foreach vs for performance test results

问题描述

有人可以解释这些结果吗？
我知道有重复的问题，但是我还没有找到一个与我的结果相同的结论：o b / b

 使用系统; 
 using System.Collections.Generic; 
使用System.Diagnostics; 
使用System.Linq; 
使用System.Text; 
使用System.Threading.Tasks; 
 
命名空间SpeedTest 
 {
类Person 
 {
 public Person（string name）
 {
 this.Name = name ; 
} 
 
 public string Name {get;组; } 
} 
 
 
 
 
 
 
 
 
 $ b $ ;（）; 
 AddTwins（FRANCISCO，people）; 
 var stopwatch = new Stopwatch（）; 
 
 string name =OCSICNARF; 
 
 long linqTime = 0L; 
 long foreachTime = 0L; 
 long forTime = 0L; 
 
 stopwatch.Start（）; 
 Person person0; 
 var result =从人中的人
 where person.Name == name 
 select person; 
 person0 = result.First（）; 
 linqTime = stopwatch.ElapsedMilliseconds; 
 stopwatch.Restart（）; 
 Person person1; 
 foreach（人员p）
 {
 if（p.Name == name）
 {
 person1 = p; 
 break; 
} 
} 
 foreachTime = stopwatch.ElapsedMilliseconds; 
 stopwatch.Restart（）; 
 Person person2; 
 for（int i = 0; i< people.Count; i ++）
 {
 if（people [i] .Name == name）
 {
 person2 = people [i]; 
 break; 
} 
} 
 forTime = stopwatch.ElapsedMilliseconds; 
 stopwatch.Stop（）; 
 
 Console.WriteLine（string.Format（LINQ took {0} ms，linqTime））; 
 Console.WriteLine（string.Format（FOREACH took {0} ms，foreachTime））; 
 Console.WriteLine（string.Format（FOR took {0} ms，forTime））; 
 
 
 static void AddTwins（string name，List< Person> people）
 {
 AddTwins（people，name，）; 
 
 
 private static void AddTwins（List< Person> people，string choices，string selected）
 {
 if（choices.Length == 0）
 {
 people.Add（new Person（selected））; 
 
 
 
（int i = 0; i  {
 //选择
 char c = choices [i]; 
 string select1 = choices.Substring（0，i）; 
 string choose2 = choices.Substring（i + 1）; 
 choices = choose1 + choose2; 
 
 //探索
 AddTwins（人物，选择，选择+ c）; 
 
 //取消选择
字符串unchoose1 = choices.Substring（0，i）; 
 string unchoose2 = choices.Substring（i）; 
 choices = unchoose1 + c + unchoose2; 
 
 
 
 
 $ b code $ 
 
 
 
 
解决方案
您从不执行 LINQ 查询，您只需创建它。您应该使用 ToList 或 ToArray 方法来强制迭代，可能您不会得到不同的结果，因为 LINQ 还使用了一个 foreach 循环。 
 
 
 编辑： LINQ 需要多一点时间，因为您正在遍历所有项目。但是在另外两个循环中，只要你找到一个匹配，你就打破了循环。尝试使用 FirstOrDefault 而不是 Where ，您应该得到相同的（或类似的）结果。
  people.FirstOrDefault（p => p.Name == name）; 
  
 
Could somebody explain these results?
I know there are duplicate questions, but I have yet to find a single question that came to the same conclusion as my results :o
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SpeedTest
{
    class Person
    {    
        public Person(string name)
        {
            this.Name = name;
        }

        public string Name { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var people = new List<Person>();
            AddTwins("FRANCISCO", people);
            var stopwatch = new Stopwatch();

            string name = "OCSICNARF";

            long linqTime = 0L;
            long foreachTime = 0L;
            long forTime = 0L;

            stopwatch.Start();
            Person person0;
            var result = from person in people
                         where person.Name == name
                         select person;
            person0 = result.First();
            linqTime = stopwatch.ElapsedMilliseconds;
            stopwatch.Restart();
            Person person1;
            foreach (Person p in people)
            {
                if (p.Name == name)
                {
                    person1 = p;
                    break;
                }
            }
            foreachTime = stopwatch.ElapsedMilliseconds;
            stopwatch.Restart();
            Person person2;
            for (int i = 0; i < people.Count; i++)
            {
                if (people[i].Name == name)
                {
                    person2 = people[i];
                    break;
                }
            }
            forTime = stopwatch.ElapsedMilliseconds;
            stopwatch.Stop();

            Console.WriteLine(string.Format("LINQ took {0}ms", linqTime));
            Console.WriteLine(string.Format("FOREACH took {0}ms", foreachTime));
            Console.WriteLine(string.Format("FOR took {0}ms", forTime));
        }

        static void AddTwins(string name, List<Person> people)
        {
            AddTwins(people, name, "");
        }

        private static void AddTwins(List<Person> people, string choices, string chosen)
        {
            if (choices.Length == 0)
            {
                people.Add(new Person(chosen));
            }
            else
            {
                for (int i = 0; i < choices.Length; i++)
                {
                    // choose
                    char c = choices[i];
                    string choose1 = choices.Substring(0, i);
                    string choose2 = choices.Substring(i + 1);
                    choices = choose1 + choose2;

                    // explore
                    AddTwins(people, choices, chosen + c);

                    // Unchoose
                    string unchoose1 = choices.Substring(0, i);
                    string unchoose2 = choices.Substring(i);
                    choices = unchoose1 + c + unchoose2;
                }
            }
        }
    }
}
解决方案
You never execute the LINQ query, you just create it. You should use ToList or ToArray method to force an iteration, probably you won't get a different result because LINQ uses a foreach loop as well.


Edit: LINQ takes a little bit more time because you are iterating over all of the items. But in your other two loops you are breaking the loop as soon as you find a match. Try using FirstOrDefault instead of Where and you should get the same (or similar) result.
people.FirstOrDefault(p => p.Name == name);


                        
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