c# - 查找两个字典的交集

Question

我有两个字典，比如 Dic1<string,string>和 Dic2<string,string>我想生成一个新的 list Dic1 中存在的键的值和 Dic2所以例如如果

Dic1: <12,"hi">, <14,"bye">
Dic2: <12,"hello">, <18,"bye">

那么列表应该是:"hi" , "hello"

我尝试使用 Dic1.Keys.Intersect但还不太明白。

What I tried: Dic1.Keys.Intersect(Dic2.Keys).ToList(t => t.Values);

Answer 1

给你:

var dic1 = new Dictionary<int, string> { { 12, "hi" }, { 14, "bye" } };
var dic2 = new Dictionary<int, string> { { 12, "hello" }, { 18, "bye" } };
HashSet<int> commonKeys = new HashSet<int>(dic1.Keys);
commonKeys.IntersectWith(dic2.Keys);
var result = 
    dic1
    .Where(x => commonKeys.Contains(x.Key))
    .Concat(dic2.Where(x => commonKeys.Contains(x.Key)))
    // .Select(x => x.Value) // With this additional select you'll get only the values.
    .ToList();

结果列表包含{ 12, "hi" }和 { 12, "hello" }

HashSet对于十字路口非常有用。

---

出于好奇，我比较了所有六个解决方案(希望没有遗漏任何一个)，时间如下:

@EZI        Intersect2   GroupBy         ~149ms
@Selman22   Intersect3   Keys.Intersect   ~41ms
@dbc        Intersect4   Where1           ~22ms
@dbc        Intersect5   Where2           ~18ms
@dbc        Intersect5   Classic          ~11ms
@t3chb0t    Intersect1   HashSet          ~66ms

---

class Program
{
    static void Main(string[] args)
    {
        var dic1 = new Dictionary<int, string>();
        var dic2 = new Dictionary<int, string>();

        Random rnd = new Random(DateTime.Now.Millisecond);
        for (int i = 0; i < 100000; i++)
        {
            int id = 0;

            do { id = rnd.Next(0, 1000000); } while (dic1.ContainsKey(id));
            dic1.Add(id, "hi");

            do { id = rnd.Next(0, 1000000); } while (dic2.ContainsKey(id));
            dic2.Add(id, "hello");
        }

        List<List<string>> results = new List<List<string>>();

        using (new AutoStopwatch(true)) { results.Add(Intersect1(dic1, dic2)); }
        Console.WriteLine("Intersect1 elapsed in {0}ms (HashSet)", AutoStopwatch.Stopwatch.ElapsedMilliseconds);

        using (new AutoStopwatch(true)) { results.Add(Intersect2(dic1, dic2)); }
        Console.WriteLine("Intersect2 elapsed in {0}ms (GroupBy)", AutoStopwatch.Stopwatch.ElapsedMilliseconds);

        using (new AutoStopwatch(true)) { results.Add(Intersect3(dic1, dic2)); }
        Console.WriteLine("Intersect3 elapsed in {0}ms (Keys.Intersect)", AutoStopwatch.Stopwatch.ElapsedMilliseconds);

        using (new AutoStopwatch(true)) { results.Add(Intersect4(dic1, dic2)); }
        Console.WriteLine("Intersect4 elapsed in {0}ms (Where1)", AutoStopwatch.Stopwatch.ElapsedMilliseconds);

        using (new AutoStopwatch(true)) { results.Add(Intersect5(dic1, dic2)); }
        Console.WriteLine("Intersect5 elapsed in {0}ms (Where2)", AutoStopwatch.Stopwatch.ElapsedMilliseconds);

        using (new AutoStopwatch(true)) { results.Add(Intersect7(dic1, dic2)); }
        Console.WriteLine("Intersect7 elapsed in {0}ms (Old style :-)", AutoStopwatch.Stopwatch.ElapsedMilliseconds);

        Console.ReadKey();
    }

    static List<string> Intersect1(Dictionary<int, string> dic1, Dictionary<int, string> dic2)
    {
        HashSet<int> commonKeys = new HashSet<int>(dic1.Keys);
        commonKeys.IntersectWith(dic2.Keys);
        var result =
            dic1
            .Where(x => commonKeys.Contains(x.Key))
            .Concat(dic2.Where(x => commonKeys.Contains(x.Key)))
            .Select(x => x.Value)
            .ToList();
        return result;
    }

    static List<string> Intersect2(Dictionary<int, string> dic1, Dictionary<int, string> dic2)
    {
        var result = dic1.Concat(dic2)
                    .GroupBy(x => x.Key)
                    .Where(g => g.Count() > 1)
                    .SelectMany(g => g.Select(x => x.Value))
                    .ToList();
        return result;
    }

    static List<string> Intersect3(Dictionary<int, string> dic1, Dictionary<int, string> dic2)
    {
        var result =
            dic1
            .Keys
            .Intersect(dic2.Keys)
            .SelectMany(key => new[] { dic1[key], dic2[key] })
            .ToList();
        return result;
    }

    static List<string> Intersect4(Dictionary<int, string> dic1, Dictionary<int, string> dic2)
    {
        var result =
            dic1.
            Where(pair => dic2.ContainsKey(pair.Key))
            .SelectMany(pair => new[] { dic2[pair.Key], pair.Value }).ToList();
        return result;
    }

    static List<string> Intersect5(Dictionary<int, string> dic1, Dictionary<int, string> dic2)
    {
        var result =
            dic1
            .Keys
            .Where(dic2.ContainsKey).SelectMany(k => new[] { dic1[k], dic2[k] })
            .ToList();
        return result;
    }

    static List<string> Intersect7(Dictionary<int, string> dic1, Dictionary<int, string> dic2)
    {
        var list = new List<string>();
        foreach (var key in dic1.Keys)
        {
            if (dic2.ContainsKey(key))
            {
                list.Add(dic1[key]);
                list.Add(dic2[key]);
            }
        }
        return list;
    }
}

class AutoStopwatch : IDisposable
{
    public static readonly Stopwatch Stopwatch = new Stopwatch();

    public AutoStopwatch(bool start)
    {
        Stopwatch.Reset();
        if (start) Stopwatch.Start();
    }
    public void Dispose()
    {
        Stopwatch.Stop();
    }
}