字典查找、linq、foreach、yield等几种查找性能对比

先上代码，以1千万记录的内存查找测试：

 List<Student> stuList = new List<Student>();
            Dictionary<int, Student> dictStu = new Dictionary<int, Student>();
            Student student = null;
            for (int i = 0; i < 10000000; i++)
            {
                student = new Student(i);
                stuList.Add(student);
                dictStu.Add(i, student);
            }
            Stopwatch sw = new Stopwatch();
            sw.Start();
            student = dictStu[99999];
            sw.Stop();
            Console.WriteLine(student.ToString());
            Console.WriteLine("dict={0}", sw.ElapsedMilliseconds);


            sw.Reset();
            sw.Start();

             var yieldResult = StudentResult(stuList);
             foreach (Student stu in yieldResult)
             {
                 Console.WriteLine(stu.ToString());
             }
            // Student s = yieldResult.First<Student>();
            //Console.WriteLine(s.ToString());
            sw.Stop();

            Console.WriteLine("yieldResult={0}", sw.ElapsedMilliseconds);

            sw.Reset();
            sw.Start();

            foreach (Student stu in stuList)
            {
                if (stu.Age == 99999)
                {
                    student = stu;
                    break;
                }
            }


            sw.Stop();

            Console.WriteLine("foreach={0}", sw.ElapsedMilliseconds);



            sw.Reset();
            sw.Start();

            var result = from stu in stuList
                         where stu.Age == 99999
                         select stu;

            foreach (Student stu in result)
            {
                Console.WriteLine(stu.ToString());
            }
            sw.Stop();

            Console.WriteLine("linq={0}", sw.ElapsedMilliseconds);

    static IEnumerable<Student> StudentResult(List<Student> stuList)
        {
            foreach (Student stu in stuList)
            {
                if (stu.Age == 99999)
                {
                    yield return stu;
                }

            }
        }

执行结果

结论：

字典查找为哈希查找，性能最优，其次是foreach遍历，后依次为yield，linq

//var result = from stu in stuList
// //where stu.Age > 10 && stu.Age < 20
// select stu;

var result = stuList
.Where(r => r.Age > 10 && r.Age < 20)
.Select(r => r);