linq過濾使訂單保持不變

Question

如何過濾列表，使過濾順序在輸出中保持不變。

void Main() 
{ 
    var states = new List<State>() { new State("CA", "California"), 
            new State("NY", "New York"), 
            new State("AL", "Alabama"), 
            new State("NV", "Nevada")}; 
    var myOrder = new List<string>() {"AL", "NY"}; 

    var result = states.Where(s => myOrder.Exists(c => string.Equals(c, s.Code, StringComparison.OrdinalIgnoreCase))); 
    foreach(var res in result) 
    { 
     Console.WriteLine(res.Code); 
    } 
    //this outputs - NY AL 
} 

public class State 
{ 
    public string Code; 
    public string Name; 
    public State(string code, string name) 
    { 
     Code = code; 
     Name = name; 
    } 
} 

我需要輸出的順序與myOrder列表（預期輸出 - AL NY）中給出的順序相同。

Answer 1

添加條件OrderBy正確：

.OrderBy(s => myOrder.IndexOf(s.Code)); 

你的條件爲：

var result = states 
    .Where(s => myOrder.Exists(c => string.Equals(c, s.Code, StringComparison.OrdinalIgnoreCase))) 
    .OrderBy(s => myOrder.IndexOf(s.Code)); 

Dotnet Fiddle Demo

Answer 2

如果我理解正確，你想要什麼，一個連接會這麼做：

static void Main() 
{ 
    //below is a database call, for sake of code simplicity, I have hardcoded few data samples. 
    var states = new List<State>() { 
      new State("CA", "California"), 
      new State("NY", "New York"), 
      new State("AL", "Alabama"), 
      new State("NV", "Nevada") 
     }; 

    var myOrder = new List<string>() { "AL", "DE", "NY", "TX" }; 

    // Join myOrder... 
    var result = myOrder.Join(
     // to states... 
     states, 
     // ...on the whole myOrder item... 
     o => o, 
     // ...equals the Code field of the State 
     s => s.Code, 
     // And the result of the join is just the State 
     (o, s) => s); 

    // this outputs - AL NY 

    foreach (var res in result) 
    { 
     Console.WriteLine(res.Code); 
    } 
} 

使用myOrder訂購的最簡單方法就是從那裏開始，不要更改它。有很多方法可以做到這一點，但是這會起作用。