Question

如何过滤列表，使输出中的过滤顺序保持不变。

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;
    }
}

我需要的输出顺序与myOrder列表中给出的顺序相同（预期输出 - AL NY）。

Answer 1

如果我正确理解了你想要的东西，那么联接会这样做：

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排序的最简单方法就是从那里开始，不要更改它。有很多方法可以做到这一点，但这样做有用。

Answer 2

正确地向OrderBy添加条件：

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

你的情况变成：

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

Dotnet Fiddle Demo

linq过滤使订单保持完整

2 个答案: