.net 判断list数据里是否有重复元素，使用linq

          List<Person> _list = new List<Person>();

            Person per0 = new Person();
            per0.Age = 10;
            per0.Name = "test0";
            _list.Add(per0);

            Person per1 = new Person();
            per1.Age = 11;
            per1.Name = "test1";
            _list.Add(per1);

            Person per2 = new Person();
            per2.Age = 12;
            per2.Name = "test0";
            _list.Add(per2);

            Person per3 = new Person();
            per3.Age = 13;
            per3.Name = "test3";
            _list.Add(per3);

            Person per4 = new Person();
            per4.Age = 12;
            per4.Name = "test0";
            _list.Add(per4);

            Person per5 = new Person();
            per5.Age = 13;
            per5.Name = "test3";
            _list.Add(per5);

(1)根据条件查询是否存在符合某个条件元素：

            var query = from l in _list.Where(r => r.Name == "test0" & r.Age == 12)
                        select new
                        {
                            l.Name,
                            l.Age
                        };

            int count = query.Count();
            Response.Write("Name=test0，age=12重复复元素的个数：" + count);

(2)查询list集合中存在重复元素的个数：
 var query = from l in _list
                        group l by new { l.Name } into g
                        select new
                        {
                            Name = g.Key.Name,
                            RepeatNameCount = g.Count()
                        };

            int count = 0;
            foreach (var item in query)
            {
                if (item.RepeatNameCount > 1)
                {
                    count++;
                }
            }
            Response.Write("list重复复元素的个数：" + count);