Concatenate two Dictionaries [duplicate]

Answer 1

I think you defined your GroupNames as Dictionary<string,string>, so you need to add ToDictionary like this:

GroupNames = GroupNames.Concat(AddedGroupNames)
                       .ToDictionary(x=>x.Key,x=>x.Value);

Note that 2 original dictionaries would have different keys, otherwise we need some rule to merge them correctly.