程序代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {

            int[] testDataList = new int[] { 1, 2, 3, 2, 3, 6 ,6,1,1,3,3};

            Stat1(testDataList);

            Console.WriteLine("************************");

            Stat2(testDataList);

            Console.Read();
        }

        /// <summary>
        /// 方法一
        /// </summary>
        /// <param name="testDataList"></param>
        static void Stat1(int[] testDataList)
        {
            Dictionary<int, int> statDic = new Dictionary<int, int>();
            foreach (int i in testDataList)
            {
                //还不存在于statDic中
                if (!statDic.ContainsKey(i))
                {
                    statDic.Add(i, 1);
                }
                else    //已经存在了，就在value中加一
                {
                    statDic[i] += 1;
                }
            }

            foreach (int key in statDic.Keys)
            {
                Console.WriteLine("{0} -> {1}", key.ToString(), statDic[key].ToString());
            }
        }

        /// <summary>
        /// 方法二
        /// </summary>
        /// <param name="testDataList"></param>
        static void Stat2(int[] testDataList)
        {
            List<DataT> lists = new List<DataT>();
            foreach (int i in testDataList)
            {
                DataT t = new DataT();
                t.ID = i;

                lists.Add(t);
            }

            var q = from t1 in lists
                    group t1 by t1.ID into g
                    select new
                    {
                        g.Key,
                        Stat = g.Count(p => p.ID == g.Key)
                    };

            foreach (var q1 in q)
            {
                Console.WriteLine("{0} -> {1}", q1.Key.ToString(), q1.Stat.ToString());
            }
        }
    }

    public class DataT
    {
        public int ID { get; set; }
    }
}