去除list集合中重复项的几种方法

for (int i = 0; i < li2.Count; i++) //外循环是循环的次数
{
for (int j = li2.Count - 1 ; j > i; j--) //内循环是 外循环一次比较的次数
{

if (li2[i] == li2[j])
{
li2.RemoveAt(j);
}

}
}

去掉modelList中title重复的内容，不区分大小写

class Program
    {
        static void Main(string[] args)
        {
            List<Model> modelList = new List<Model>() 
            { new Model() { ID = 1, Title = "abcde" },
                new Model() { ID = 2, Title = "ABCDE" },
                new Model(){ ID = 3, Title = "AbcdE" },
                new Model() { ID = 4, Title = "A" }, 
                new Model() { ID = 5, Title = "a" } 
            };
            Console.Read();
        }
    }
    public class Model
    {
        public int ID { get; set; }
        public string Title { get; set; }
    }

解决方案一：这里比较的前提是对象的哈希代码相等。否则不会比较，因为哈希代码不相等。两个对象显然不相等

//定义一个类继承IEqualityComparer接口
    public class ModelComparer : IEqualityComparer<Model>
    {
        public bool Equals(Model x, Model y)
        {
            return x.Title.ToUpper() == y.Title.ToUpper();
        }
        public int GetHashCode(Model obj)
        {
            return obj.Title.ToUpper().GetHashCode();
        }
    }

modelList = modelList.Distinct(new ModelComparer()).ToList();

解决方案二：

var title = modelList.GroupBy(m => m.Title.ToLower().Trim()).Select(m => new { ID = m.FirstOrDefault().ID });
            modelList = modelList.Where(m => title.Select(mo => mo.ID).Contains(m.ID)).ToList(); 
            foreach (var item in modelList)
            {
                Console.WriteLine(item.ID + "\t" + item.Title);
            }