var sessions = from s in db.Sessions where s.TheaterID == id orderby s.MovieID, s.Time select s;

public ActionResult MyAction(int id)
        {
            Theather theater = db.Theater.Find(id);
            ViewBag.TheaterName = theater.NomeCinema;
            var sessions = from s in db.Sessions where s.TheaterID == id orderby s.MovieID, s.Time select s;

            var mapMovies = new Dictionary<string, List<DateTime>>();

            foreach (Session s in sessions)
            {
                if ( !mapMovies.ContainsKey( s.Movie.MovieName ) )
                {
                    mapMovies.Add( s.Movie.MovieName, new List<DateTime>() );
                }
                mapMovies[s.Movie.MovieName].Add(s.Time);
            }
            ViewBag.MapMovies = mapMovies;
            return View();
        }