从Dictionary <Key,Item>中删除元素

Question

我有一个词典,其中的项目是(例如):

1. "A",4
2. "B",44
3. "再见",56
4. "C",99
5. "D",46
6. "6672",0

我有一个清单:

1. "一个"
2. "C"
3. "d"

我想从我的字典中删除其键不在我的列表中的所有元素,最后我的字典将是:

1. "A",4
2. "C",99
3. "D",46

我能怎么做？

Answer 1

It's simpler to construct new Dictionary to contain elements that are in the list:

List<string> keysToInclude = new List<string> {"A", "B", "C"};
var newDict = myDictionary
     .Where(kvp=>keysToInclude.Contains(kvp.Key))
     .ToDictionary(kvp=>kvp.Key, kvp=>kvp.Value);

如果修改现有字典很重要(例如,它是某个类的只读属性)

var keysToRemove = myDictionary.Keys.Except(keysToInclude).ToList();

foreach (var key in keysToRemove)
     myDictionary.Remove(key);

注意ToList()调用 - 实现要删除的键列表很重要.如果您尝试在没有实现的情况下运行代码keysToRemove,您可能会遇到类似"集合已更改"的异常.

Answer 2

// For efficiency with large lists, for small ones use myList below instead.  
var mySet = new HashSet<string>(myList);

// Create a new dictionary with just the keys in the set
myDictionary = myDictionary
               .Where(x => mySet.Contains(x.Key))
               .ToDictionary(x => x.Key, x => x.Value);

Answer 3

dict.Keys.Except(list).ToList()
    .ForEach(key => dict.Remove(key));