using System;

using System.Collections.Generic;

using System.Linq;

​

public static class Program

{

    public static void Main()

    {

        List<StudentDetails> students = new List<StudentDetails>()

        {

            new StudentDetails {StudentId = 1, StudentName = "Bill", SubjectId = 1, SubjectName = "Math", ClassId = 1, ClassName = "10A"},

            new StudentDetails {StudentId = 2, StudentName = "Fill", SubjectId = 2, SubjectName = "Literature", ClassId = 1, ClassName = "10A"},

            new StudentDetails {StudentId = 3, StudentName = "Will", SubjectId = 1, SubjectName = "Math", ClassId = 2, ClassName = "10B"},

            new StudentDetails {StudentId = 1, StudentName = "Bill", SubjectId = 3, SubjectName = "Physics", ClassId = 2, ClassName = "10B"},

            new StudentDetails {StudentId = 1, StudentName = "Bill", SubjectId = 3, SubjectName = "Physics", ClassId = 1, ClassName = "10A"}

        };

​

        List<Class> classes = students

            .GroupBy(s => s, new ComparerById<StudentDetails>(s => s.ClassId))

            .Select(c => new Class

                    {

                        ClassId = c.Key.ClassId,

                        ClassName = c.Key.ClassName,

                        Students = c

                            .GroupBy(s => s, new ComparerById<StudentDetails>(s => s.StudentId))

                            .Select(s => new Student

                                    {

                                        StudentId = s.Key.StudentId,

                                        StudentName = s.Key.StudentName,

                                        Subjects = s

                                            .GroupBy(t => t, new ComparerById<StudentDetails>(t => t.SubjectId))

                                            .Select(t => new Subject {SubjectId = t.Key.SubjectId, SubjectName = t.Key.SubjectName})

                                            .ToList()

                                    }).ToList()

                    }).ToList();

​

        foreach (Class @class in classes)

        {

            Console.WriteLine("Class({0}, {1})", @class.ClassId, @class.ClassName);

​

            foreach (Student student in @class.Students)

            {

                Console.WriteLine("\tStudent({0}, {1})", student.StudentId, student.StudentName);

​

                foreach (Subject subject in student.Subjects)

                {

                    Console.WriteLine("\t\tSubject({0}, {1})", subject.SubjectId, subject.SubjectName);

                }

            }

        }

    }

}

​

public class StudentDetails

{

    public int SubjectId { get; set; }

    public string SubjectName { get; set; }

    public int StudentId { get; set; }

    public string StudentName { get; set; }

    public int ClassId { get; set; }

    public string ClassName { get; set; }

}

​

public class Class

{

    public int ClassId { get; set; }

    public string ClassName { get; set; }

    public List<Student> Students { get; set; }

}

​

public class Student

{

    public int StudentId { get; set; }

    public string StudentName { get; set; }

    public List<Subject> Subjects { get; set; }

}

​

public class Subject

{

    public int SubjectId { get; set; }

    public string SubjectName { get; set; }

}

​

public class ComparerById<T> : IEqualityComparer<T>

{

    private readonly Func<T, int> _keySelector;

​

    public ComparerById(Func<T, int> keySelector) { _keySelector = keySelector; }

​

    public bool Equals(T x, T y) { return _keySelector(x) == _keySelector(y); }

​

    public int GetHashCode(T obj) { return _keySelector(obj); }

}