public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> enu)
        {
            T[] tmp = new T[enu.Count()];
            Random rand = new Random();
            foreach (var e in enu)
            {
                int i;
             while ( tmp[i=  rand.Next(tmp.Length)]!=null);
             tmp[i] = e;


            }
            return tmp;
        }
/////////////////////////////////////////////////////////////////
   var tmp = from zap in context.przedmiot_obieralny_zapisy group zap by zap.osoba into ocb select new { ocb.Key, ocb };

            foreach (var z in tmp.ToList())
            {
                int i=0;
                foreach (var o in z.ocb.Shuffle())
                {
                    o.priorytet = ++i;
                }
            }
            context.SaveChanges();
            return "END";