using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    class Student

    {

        public int id;

        public string studentname;

        public string subject;

        public int grade;

        public override String ToString() 

        {

            return String.Format("{0}: {1} - {2} - grade {3}", id, studentname, subject, grade);

        }

    }

    public static void Main()

    {

        var students = new[]

        {

            new Student()

            {

                id = 3,

                studentname = "harold",

                subject = "golf",

                grade = 3

            },

            new Student()

            {

                 id = 4,

                studentname = "harold",

                subject = "golf",

                grade = 3

            },

            new Student()

            {

                id = 3,

                studentname = "harold",

                subject = "golf",

                grade = 5

            },

                new Student()

            {

                id = 6,

                studentname = "sigfried",

                subject = "volleyball",

                grade = 6

            }

        };

        IEnumerable<Student> distinctStudents = students

                                                    .AsEnumerable() // Force it to use Linq to Objects (Not really necessary in this specific case, as we're already using it)

                                                    .GroupBy(s => Tuple.Create(s.studentname, s.subject, s.grade))

                                                    .Select(g => g.First());

        foreach(var student in distinctStudents)

        {

            Console.WriteLine(student);

        }

    }

}