因为用到list，要去除重复数据，尝试了几种方法。记录于此。。。
测试数据：
List<string> li1 = new List<string> { "8", "8", "9", "9" ,"0","9"};List<string> li2 = new List<string> { "张三", "张三", "李四", "张三", "王五", "李四" };List<string> li3 = new List<string> { "A", "A", "C", "A", "C", "D" };List<string> li4 = new List<string> { "12", "18", "19", "19", "10", "19" };
方法一：
HashSet<string> hs = new HashSet<string>(li1); //此时已经去掉重复的数据保存在hashset中
方法二：
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);}}}
方法三：
//把相同的用null代替。for (int i = 0; i < li3.Count; i++){for (int j = 0; j < li3.Count; j++){if (i == j) continue;if (li3[i] == li3[j]){li3[j] = "null";}}}
方法四：
//这方法跟上面的一样，只是变了逻辑for (int i = 0; i < li4.Count - 1; i++){for (int j = 0; j < li4.Count ; j++){if (i != j){if (li4[i] == li4[j]){li4[j] = "null";}}}}
最后输出看结果
Console.WriteLine("li1去除重复后的值为");hs.ToList().ForEach(item => Console.WriteLine(item));Console.WriteLine("li2去除重复后的值为");li2.ForEach(item => Console.WriteLine(item));Console.WriteLine("li3去除重复后的值为");li3.ForEach(item => Console.WriteLine(item));Console.WriteLine("li4去除重复后的值为");li4.ForEach(item => Console.WriteLine(item)); 
null我没去掉。用的时候去掉即可。
当然。还有许多办法。比如linq Distinct 等等都可以，看看网上的这个例子：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();}}
调用：
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);}
当然。如果你仅仅比较两个值是否相等。
List<string> li1 = new List<string> { "8", "8", "9", "8", "0", "9" };li1 = li1.Distinct().ToList();
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