IEnumerable 相关操作

public class Employee
    {
        public int EmployeeID { get; set; }
        public string Name { get; set; }
        public string Sex { get; set; }

        public int Age { get; set; }
        public int salary { get; set; }


        public override string ToString()
        {
            return $"{this.EmployeeID}-{Name}-{ Sex}-{ Age}-{ salary}";
        }


    }

1.groupby

 List<Employee> employees = new List<Employee>();

            employees.Add(new Employee { EmployeeID = 100001, Name = "Lily", Age = 25, salary = 3500, Sex = "女" });
            employees.Add(new Employee { EmployeeID = 100002, Name = "lucy", Age = 29, salary = 5500, Sex = "女" });
            employees.Add(new Employee { EmployeeID = 100003, Name = "Jonth", Age = 35, salary = 4500, Sex = "男" });
            employees.Add(new Employee { EmployeeID = 100004, Name = "tom", Age = 38, salary = 3900, Sex = "男" });
            employees.Add(new Employee { EmployeeID = 100005, Name = "jerry", Age = 35, salary = 4700, Sex = "女" });
            employees.Add(new Employee { EmployeeID = 100006, Name = "李四", Age = 44, salary = 7800, Sex = "男" });
            employees.Add(new Employee { EmployeeID = 100007, Name = "王五", Age = 55, salary = 8100, Sex = "男" });
            employees.Add(new Employee { EmployeeID = 100008, Name = "王二", Age = 46, salary = 6700, Sex = "男" });
            IEnumerable<IGrouping<string, Employee>> items = employees.GroupBy(e => e.Sex);
            foreach (IGrouping<string, Employee> g in items)
            {
                Console.WriteLine(g.Key);  //输出排序关键字   
                  foreach(Employee e in g)
                {
                    Console.WriteLine(e); //调用  Employee  toString()方法
                     }



            }
  

输出 ：女
100001-Lily-女-25-3500
100002-lucy-女-29-5500
100005-jerry-女-35-4700
男
100003-Jonth-男-35-4500
100004-tom-男-38-3900
100006-李四-男-44-7800
100007-王五-男-55-8100
100008-王二-男-46-6700

2.映射成新类型

即将原来集合List对象映射,匿名类型或 新类型的 List ，下面将employees 列表中的 Name,Sex,Age,Salary映射到新集合中

IEnumerable<dynamic> list = employees.Where(t => t.salary >= 5000).Select(t =>new   {  xm=t.Name,xb=t.Sex,nl=t.Age,gz=t.salary });

            string s = "";
                foreach (var item in list)
            {

                s = s + item;
            }

输出结果：

{ xm = lucy, xb = 女, nl = 29, gz = 5500 }{ xm = 李四, xb = 男, nl = 44, gz = 7800 }{ xm = 王五, xb = 男, nl = 55, gz = 8100 }{ xm = 王二, xb = 男, nl = 46, gz = 6700 }

 3.分类汇总统计  Groupby

 var lists=  employees.GroupBy(e => e.Sex).Select(t => new { 性别 = t.Key, 最高工资 = t.Max(e=>e.salary),最低工资=t.Min(e=>e.salary) ,人数=t.Count()});
            string d = "";
            foreach (var item in lists)
            { 
            d=d + item;
            }

            return Content( d);

输出：{ 性别 = 女, 最高工资 = 5500, 最低工资 = 3500, 人数 = 3 }{ 性别 = 男, 最高工资 = 8100, 最低工资 = 3900, 人数 = 5 }

4.自定义MySelect

static class  my{

      public  static IEnumerable<dynamic> MySelect(this IEnumerable<Employee> list, Func<Employee, dynamic> f)
        {
            List<dynamic>ml= new List<dynamic>();
            
            foreach (Employee e in list)
            {
                var t = f(e);
                ml.Add(t);

            }
           
            return ml;
        }

    }

var tlist=    employees.Where(t=>t.Age>35).MySelect(t => new { xb = t.Sex, xm = t.Name, bh = t.EmployeeID,nl=t.Age });
            string m = "";
            foreach (var item in tlist)
            { 
            m=m+item;
            }

  Console.WriteLine(m);