using System.Linq;

            int[] arr = new int[10] { 1, 2, 3, 3, 4, 2, 4, 5, 7, 8 };
            var vs = from i in arr group i by i into m select new { m.Key, num = m.Count() };
            foreach (var v in vs)
            {
                MessageBox.Show(v.Key + "=" + v.num);
            }