Linq Lambda 中group by多列后count数量的写法

直接上代码：

            List<Student> ss = new List<Student>();
            Student ss1 = new Student() { Id = 1, Age = 1, Name = "11" };
            Student ss2 = new Student() { Id = 1, Age = 1, Name = "11" };
            Student ss3 = new Student() { Id = 2, Age = 2, Name = "22" };
            Student ss4 = new Student() { Id = 2, Age = 2, Name = "22" };
            Student ss5 = new Student() { Id = 2, Age = 2, Name = "22" };
            Student ss6 = new Student() { Id = 3, Age = 3, Name = "33" };
            ss.Add(ss1);
            ss.Add(ss2);
            ss.Add(ss3);
            ss.Add(ss4);
            ss.Add(ss5);
            ss.Add(ss6);
　　　　　　　// 注意select中的Count()方法必须定义成员名称，否则会报无效的匿名成员声明。
            var aa = ss.GroupBy(m => new { m.Id, m.Age }).Select(group => new {group.Key.Id,group.Key.Age,count = group.Count()}).ToList();
            foreach (var item in aa)
            {
                Console.WriteLine(item.Id + "||" + item.Age + "||" + item.count);
            }
            Console.ReadKey();


//结果
            1 || 1 || 2
            2 || 2 || 3
            3 || 3 || 1