C＃等效于python的defaultdict（对于列表）c＃[重复]

Question

c＃等效的做法是什么：

>>> from collections import defaultdict
>>> dct = defaultdict(list)
>>> dct['key1'].append('value1')
>>> dct['key1'].append('value2')
>>> dct
defaultdict(<type 'list'>, {'key1': ['value1', 'value2']})

现在，我有：

Dictionary<string, List<string>> dct = new Dictionary<string, List<string>>();
dct.Add("key1", "value1");
dct.Add("key1", "value2");

但会出现诸如“最佳超载方法匹配的参数无效”之类的错误。

Answer 1

public static class Extensions
{
    public static void AddOrUpdate<TKey, TValue>(this Dictionary<TKey, List<TValue>> dictionary, TKey key, TValue value)
    {
        if (dictionary.ContainsKey(key))
        {
            dictionary[key].Add(value);
        }
        else
        {
            dictionary.Add(key, new List<TValue>{value});
        }
    }
}

usage：

Dictionary<string, List<string>> dct = new Dictionary<string, List<string>>();
dct.AddOrUpdate("key1", "value1");
dct.AddOrUpdate("key1", "value2");

您的第一步应该是用指定的密钥创建记录。然后，您可以在值列表中添加其他值：

Answer 2

Dictionary<string, List<string>> dct = new Dictionary<string, List<string>>();
            
List<string> mList;
if (!dct.TryGetValue("key1", out mList))
{
    mList = new List<string>();
    dct.Add("key1", mList);
}

mList.Add("value1");
mList.Add("value2");

Answer 3