Comparing two Dictionary of Dictionaries

I asked a similar question earlier in the week but I don't think my original description of the problem was very coherent, so I am trying again.

I have the following Dictionaries:

public Dictionar开发者_开发技巧y<string, List<DateTime>> 1stDict = new Dictionary<string, List<DateTime>>();

Dictionary<string, Dictionary<DateTime, double>> 2ndDict= new Dictionary<string, Dictionary<DateTime, double>>();

I need to create a third Dictionary

Dictionary<string, Dictionary<DateTime, double>> 3rdDict= new Dictionary<string, Dictionary<DateTime, double>>();

Containing Dictionaries with values from 2ndDict where DateTime does not exist in 1stDict.

I've made some attempts using nested foreach statements but having no luck.

Any advice?

Thanks, Brian.

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var thirdDict = secondDict.ToDictionary(
    x => x.Key, 
    x => x.Value.Keys.Except(firstDict[x.Key]).ToDictionary(y => y, y => x.Value[y]));