using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        List<Profile> profiles = new List<Profile>();

        profiles.Add(new Profile() { profilename = "prof1", score = 15, date = new DateTime(2015, 10, 01) });

        profiles.Add(new Profile() { profilename = "prof1", score = 15, date = new DateTime(2015, 10, 02) });

        profiles.Add(new Profile() { profilename = "prof1", score = 18, date = new DateTime(2015, 10, 03) });

        profiles.Add(new Profile() { profilename = "prof1", score = 24, date = new DateTime(2015, 10, 25) });

        profiles.Add(new Profile() { profilename = "prof2", score = 69, date = new DateTime(2015, 10, 01) });

        profiles.Add(new Profile() { profilename = "prof2", score = 70, date = new DateTime(2015, 10, 02) });

        profiles.Add(new Profile() { profilename = "prof3", score = 115, date = new DateTime(2015, 10, 01) });

        profiles.Add(new Profile() { profilename = "prof3", score = 115, date = new DateTime(2015, 10, 02) });

        profiles.Add(new Profile() { profilename = "prof2", score = 73, date = new DateTime(2015, 10, 03) });

        profiles.Add(new Profile() { profilename = "prof3", score = 119, date = new DateTime(2015, 10, 03) });

        profiles.Add(new Profile() { profilename = "prof2", score = 98, date = new DateTime(2015, 10, 25) });

        profiles.Add(new Profile() { profilename = "prof3", score = 187, date = new DateTime(2015, 10, 25) });

        var result = profiles

            .GroupBy(p => p.profilename)

            .Select(g => new {

                profilename = g.Key,

                firstscore = g.OrderBy(p => p.date).First().score,

                lastscore = g.OrderByDescending(p => p.date).First().score

            })

            .Select(x => new { x.profilename, diff = x.lastscore - x.firstscore })

            .ToList();

        foreach (var item in result)

        {

            Console.WriteLine(item);

        }

    }

    class Profile

    {

        public string profilename { get; set; }

        public DateTime date { get; set; }

        public int score { get; set; }

    }

}