在c#中合并2个或更多字典(Dictionary<TKey, TValue>)的最佳方法是什么? (像LINQ这样的3.0特性就可以了)。

我正在考虑一个方法签名,如下所示:

public static Dictionary<TKey,TValue>
                 Merge<TKey,TValue>(Dictionary<TKey,TValue>[] dictionaries);

or

public static Dictionary<TKey,TValue>
                 Merge<TKey,TValue>(IEnumerable<Dictionary<TKey,TValue>> dictionaries);

关于重复键的处理:在发生冲突的情况下,保存到字典中的值并不重要,只要它是一致的。


当前回答

如果有多个键(“右”键取代“左”键),这不会爆炸,可以合并一些字典(如果需要),并保留类型(限制它需要一个有意义的默认公共构造函数):

public static class DictionaryExtensions
{
    // Works in C#3/VS2008:
    // Returns a new dictionary of this ... others merged leftward.
    // Keeps the type of 'this', which must be default-instantiable.
    // Example: 
    //   result = map.MergeLeft(other1, other2, ...)
    public static T MergeLeft<T,K,V>(this T me, params IDictionary<K,V>[] others)
        where T : IDictionary<K,V>, new()
    {
        T newMap = new T();
        foreach (IDictionary<K,V> src in
            (new List<IDictionary<K,V>> { me }).Concat(others)) {
            // ^-- echk. Not quite there type-system.
            foreach (KeyValuePair<K,V> p in src) {
                newMap[p.Key] = p.Value;
            }
        }
        return newMap;
    }

}

其他回答

其平凡解为:

using System.Collections.Generic;
...
public static Dictionary<TKey, TValue>
    Merge<TKey,TValue>(IEnumerable<Dictionary<TKey, TValue>> dictionaries)
{
    var result = new Dictionary<TKey, TValue>();
    foreach (var dict in dictionaries)
        foreach (var x in dict)
            result[x.Key] = x.Value;
    return result;
}
Dictionary<String, String> allTables = new Dictionary<String, String>();
allTables = tables1.Union(tables2).ToDictionary(pair => pair.Key, pair => pair.Value);

与之前没有LINQ的情况下再次简化,如果存在则使用bool默认值非破坏性合并,如果为true则完全覆盖,而不是使用enum。它仍然适合我自己的需要,而不需要任何花哨的代码:

using System.Collections.Generic;
using System.Linq;

public static partial class Extensions
{
    public static void Merge<K, V>(this IDictionary<K, V> target, 
                                   IDictionary<K, V> source, 
                                   bool overwrite = false)
    {
        foreach (KeyValuePair _ in source)
            if (overwrite || !target.ContainsKey(_.Key))
                target[_.Key] = _.Value;
    }
}

如何添加一个参数重载?

此外,您应该将它们输入为dictionary以获得最大的灵活性。

public static IDictionary<TKey, TValue> Merge<TKey, TValue>(IEnumerable<IDictionary<TKey, TValue>> dictionaries)
{
    // ...
}

public static IDictionary<TKey, TValue> Merge<TKey, TValue>(params IDictionary<TKey, TValue>[] dictionaries)
{
    return Merge((IEnumerable<TKey, TValue>) dictionaries);
}
using System.Collections.Generic;
using System.Linq;

public static class DictionaryExtensions
{
    public enum MergeKind { SkipDuplicates, OverwriteDuplicates }
    public static void Merge<K, V>(this IDictionary<K, V> target, IDictionary<K, V> source, MergeKind kind = MergeKind.SkipDuplicates) =>
        source.ToList().ForEach(_ => { if (kind == MergeKind.OverwriteDuplicates || !target.ContainsKey(_.Key)) target[_.Key] = _.Value; });
}

你可以跳过/忽略(默认)或覆盖副本:如果你对Linq性能不过分挑剔,而是像我一样喜欢简洁的可维护代码:在这种情况下,你可以删除默认的MergeKind。skipduplicate用于强制调用者进行选择,并使开发人员知道结果将是什么!