c# dictionaries intersect

c#, dictionary, intersect, key

Solution

You could do in this way:

resultDict =  primaryDict.Keys.Intersect(secondaryDict.Keys)
                              .ToDictionary(t => t, t => primaryDict[t]);

or, alternatively:

resultDict =  primaryDict.Where(x => secondaryDict.ContainsKey(x.Key))
                         .ToDictionary(x => x.Key, x => x.Value);

the latter maybe is slightly more efficient because avoids the creation of a throw-away collection (the one generated by the Intersect method) and does not require a second access-by-key to `primaryDict`.

EDIT (as per comment) :

resultDict =  
primaryDict.Where(x => secondaryDict.ContainsKey(x.Key))
           .ToDictionary(x => x.Key, x => x.Value + secondaryDict[x.Key]);

Problem

I have a question about Linq / Lambda and the following issue: I have two dictionaries, primary and secondary... These two dictionaries are defined as Key=string, Value=int. I need to trim down the primary dictionary if the KEYS intersect with secondary dictionary. i.e.: ``` primaryDict = ["thing1", 33] ["thing2", 24] ["thing3", 21] ["thing4", 17] ["thing5", 12] secondaryDict = ["thing1", 22] ["thing3", 20] ["thing4", 19] ["thing7", 17] ["thing9", 10] resultDict = ["thing1", 33] ["thing3", 21] ["thing4", 17] ``` My attempt: ``` resultDict = primaryDict.Keys.Intersect(secondaryDict.Keys).ToDictionary(t => t.Key, t.Value); ``` This obviously does not work because the primaryDict.Keys.Intersect is returning a list of keys... how would I reestablish a new dictionary, or pair down the primary dictionary? Any help would be appreciated.

Original source