因為用到list，要去除重復數據，嘗試了幾種方法。記錄于此。。。
測試數據：
List<string> li1 = new List<string> { "8", "8", "9", "9" ,"0","9"};List<string> li2 = new List<string> { "張三", "張三", "李四", "張三", "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); //此時已經去掉重復的數據保存在hashset中
方法二：
for (int i = 0; i < li2.Count; i++) //外循環是循環的次數 {for (int j = li2.Count - 1 ; j > i; j--) //內循環是 外循環一次比較的次數 {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：
//這方法跟上面的一樣，只是變了邏輯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";}}}}
最后輸出看結果
Console.WriteLine("li1去除重復后的值為");hs.ToList().ForEach(item => Console.WriteLine(item));Console.WriteLine("li2去除重復后的值為");li2.ForEach(item => Console.WriteLine(item));Console.WriteLine("li3去除重復后的值為");li3.ForEach(item => Console.WriteLine(item));Console.WriteLine("li4去除重復后的值為");li4.ForEach(item => Console.WriteLine(item)); 
null我沒去掉。用的時候去掉即可。
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當然。還有許多辦法。比如linq? Distinct? 等等都可以，看看網上的這個例子：去掉modelList中title重復的內容，不區分大小寫
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; }}
解決方案一：這里比較的前提是對象的哈希代碼相等。否則不會比較，因為哈希代碼不相等。兩個對象顯然不相等
//定義一個類繼承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();}}
調用：
modelList = modelList.Distinct(new ModelComparer()).ToList(); 解決方案二：
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);}
當然。如果你僅僅比較兩個值是否相等。
List<string> li1 = new List<string> { "8", "8", "9", "8", "0", "9" };li1 = li1.Distinct().ToList();
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