using System;

using System.Linq;

using System.Collections.Generic;

public static class Program

{

    public static void Main()

    {

        var joinTable = SeedJoinTable();

        var query = joinTable

        .GroupBy(jt => jt.StudentId, jt => jt.LectureId)

        .Select(x => 

             new {

            StudentId = x.Key,

            CountStudentId = x.Count(),

            LectureIds = x.GroupBy(y => y),

        });

        // this is just the printing of the results

        Console.WriteLine(

            "StudentId".PadRight(15) +

            "LectureId".PadRight(15) +

            "CountStudentId".PadRight(17) +

            "CountStudentLectureId".PadRight(15));

        foreach(var x in query)

        {

            foreach(var lectureId in x.LectureIds)

            {

                Console.WriteLine(string.Format("{0}{1}{2}{3}", 

                    x.StudentId.ToString().PadRight(15), 

                    lectureId.Key.ToString().PadRight(15), 

                    x.CountStudentId.ToString().PadRight(17), 

                    lectureId.Count().ToString().PadRight(15)));

            }

        }

    }

    public static List<JoinTable> SeedJoinTable()

    {

        var list = new List<JoinTable>();

        var studentId = 0;

        var lectureId = 0;

        // insert 20 records

        for(int i = 0; i < 20; ++i)

        {

            if(i != 0)

            {

                if(i % 10 == 0) 

                {   

                    // 10 of each studentId

                    ++studentId;

                    lectureId = 0;

                }

                if(i % 3 == 0)

                {

                    // 3 of each lectureId per student

                    ++lectureId;

                }

            }

            list.Add(new JoinTable() { 

                StudentId = studentId, 

                LectureId = lectureId 

            });

        }

        return list;

    }

    public class JoinTable

    {

        public int StudentId { get; set; }

        public int LectureId { get; set; }

    }

}