LINQ:GroupBy

一、数据准备

public class Student
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Gender { get; set; }
        public string Branch { get; set; }
        public int Age { get; set; }
        public static List<Student> GetAllStudents()
        {
            return new List<Student>()
        {
            new Student { ID = 1001, Name = "玲玲", Gender = "Female",
                                         Branch = "CSE", Age = 20 },
            new Student { ID = 1002, Name = "张三", Gender = "Male",
                                         Branch = "ETC", Age = 21  },
            new Student { ID = 1003, Name = "李四", Gender = "Male",
                                         Branch = "CSE", Age = 21  },
            new Student { ID = 1004, Name = "王五", Gender = "Male",
                                         Branch = "CSE", Age = 20  },
            new Student { ID = 1005, Name = "珊珊", Gender = "Female",
                                         Branch = "ETC", Age = 20 },
            new Student { ID = 1006, Name = "涵涵", Gender = "Female",
                                         Branch = "CSE", Age = 21 },
            new Student { ID = 1007, Name = "钱六", Gender = "Male",
                                         Branch = "CSE", Age = 22  },
            new Student { ID = 1008, Name = "婷婷", Gender = "Female",
                                         Branch = "CSE", Age = 20  },
            new Student { ID = 1009, Name = "兰兰", Gender = "Female",
                                         Branch = "ETC", Age = 22 },
            new Student { ID = 1010, Name = "黄九", Gender = "Male",
                                         Branch = "ETC", Age = 21 }
        };
        }
    }

二、GroupBy

法一Query Syntax

//Using Query Syntax
            Console.WriteLine("方式一：");
            var GroupByQs = from std in Student.GetAllStudents()
                            group std by std.Branch;
            foreach (var group in GroupByQs)
            {
                Console.WriteLine(group.Key + " : " + group.Count());
                //Iterate through each student of a group
                foreach (var student in group)
                {
                    Console.WriteLine("  Name :" + student.Name + ", Age: " + student.Age + ", Gender :" + student.Gender);
                }
            }

法二Method Syntax

  Console.WriteLine("方式二：");
            var GroupByMS = Student.GetAllStudents().GroupBy(s => s.Branch);
            //It will iterate through each groups
            foreach (var group in GroupByMS)
            {
                Console.WriteLine(group.Key + " : " + group.Count());
                //Iterate through each student of a group
                foreach (var student in group)
                {
                    Console.WriteLine("  Name :" + student.Name + ", Age: " + student.Age + ", Gender :" + student.Gender);
                }
            }

三、测试结果

 

四、参考网址

https://dotnettutorials.net/lesson/groupby-in-linq/

个人代码见....CSharpBasic\LINQTutorial..