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

我将分解@orip的简单而非垃圾的创建解决方案,以提供除了Merge()之外的一个适当的AddAll()来处理将一个字典添加到另一个字典的简单情况。

using System.Collections.Generic;
...
public static Dictionary<TKey, TValue>
    AddAll<TKey,TValue>(Dictionary<TKey, TValue> dest, Dictionary<TKey, TValue> source)
{
    foreach (var x in source)
        dest[x.Key] = x.Value;
}

public static Dictionary<TKey, TValue>
    Merge<TKey,TValue>(IEnumerable<Dictionary<TKey, TValue>> dictionaries)
{
    var result = new Dictionary<TKey, TValue>();
    foreach (var dict in dictionaries)
        result.AddAll(dict);
    return result;
}

其他回答

对于c#新手来说,我害怕看到复杂的答案。

这里有一些简单的答案。 合并d1 d2,等等。字典和处理任何重叠键(“b”在下面的例子中):

示例1

{
    // 2 dictionaries,  "b" key is common with different values

    var d1 = new Dictionary<string, int>() { { "a", 10 }, { "b", 21 } };
    var d2 = new Dictionary<string, int>() { { "c", 30 }, { "b", 22 } };

    var result1 = d1.Concat(d2).GroupBy(ele => ele.Key).ToDictionary(ele => ele.Key, ele => ele.First().Value);
    // result1 is  a=10, b=21, c=30    That is, took the "b" value of the first dictionary

    var result2 = d1.Concat(d2).GroupBy(ele => ele.Key).ToDictionary(ele => ele.Key, ele => ele.Last().Value);
    // result2 is  a=10, b=22, c=30    That is, took the "b" value of the last dictionary
}

示例2

{
    // 3 dictionaries,  "b" key is common with different values

    var d1 = new Dictionary<string, int>() { { "a", 10 }, { "b", 21 } };
    var d2 = new Dictionary<string, int>() { { "c", 30 }, { "b", 22 } };
    var d3 = new Dictionary<string, int>() { { "d", 40 }, { "b", 23 } };

    var result1 = d1.Concat(d2).Concat(d3).GroupBy(ele => ele.Key).ToDictionary(ele => ele.Key, ele => ele.First().Value);
    // result1 is  a=10, b=21, c=30, d=40    That is, took the "b" value of the first dictionary

    var result2 = d1.Concat(d2).Concat(d3).GroupBy(ele => ele.Key).ToDictionary(ele => ele.Key, ele => ele.Last().Value);
    // result2 is  a=10, b=23, c=30, d=40    That is, took the "b" value of the last dictionary
}

对于更复杂的场景,请参见其他答案。 希望这有帮助。

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;
    }
}

or :

public static IDictionary<TKey, TValue> Merge<TKey, TValue>( IDictionary<TKey, TValue> x, IDictionary<TKey, TValue> y)
    {
        return x
            .Except(x.Join(y, z => z.Key, z => z.Key, (a, b) => a))
            .Concat(y)
            .ToDictionary(z => z.Key, z => z.Value);
    }

结果是一个联合,对于重复的条目,“y”胜出。

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;
}

试试

namespace Extensions
{
    public static class DictionaryExtensions
    {
        public static Dictionary<T, Y> MergeWith<T, Y>(this Dictionary<T, Y> dictA,
            Dictionary<T, Y> dictB)
        {
            foreach (var item in dictB)
            {
                if (dictA.ContainsKey(item.Key))
                    dictA[item.Key] = item.Value;
                else
                    dictA.Add(item.Key, item.Value);
            }
            return dictA;
        }
    }
}

当你想合并两个字典时

    var d1 = new Dictionary<string, string>();
    var d2 = new Dictionary<string, string>();
    d1.MergeWith(d2);