.net - How do I sum values from two dictionaries in C#?

Question

I have two dictionaries with the same structure:

Dictionary<string, int> foo = new Dictionary<string, int>() 
{
    {"Table", 5 },
    {"Chair", 3 },
    {"Couch", 1 }
};

Dictionary<string, int> bar = new Dictionary<string, int>() 
{
    {"Table", 4 },
    {"Chair", 7 },
    {"Couch", 8 }
};

I'd like to sum the values of the dictionaries together and return a third dictionaries with the keys, and the total values for each key:

Table, 9
Chair, 10
Couch, 9

My current solution is to loop through the dictionary and pull them out that way, but I know that solution isn't the most performant or most readable. However, I'm hitting a brick wall trying to come up with a solution in LINQ.

Answer 1

The following isn't the most efficient solution (because it simply treats both dictionaries as enumerables), but it will work and it is quite clear:

Dictionary<string, int> result = (from e in foo.Concat(bar)
              group e by e.Key into g
              select new { Name = g.Key, Count = g.Sum(kvp => kvp.Value) })
              .ToDictionary(item => item.Name, item => item.Count);