Merging Dictonaries in C# using LINQ

Question

i\'ve three Dictonaries like

Dictionary> D1 = new Dictionary>(); 
Dictionary

        

Answer 1

Something like this (maybe needs optimisation)?

     var lr =
    (from gr in
        (from pair in D1.Union(D2).Union(D3)
         group pair by pair.Key)
     select new KeyValuePair<int, IEnumerable<List<string>>>(gr.Key, gr.Select(x => x.Value))
    ).ToDictionary(k => k.Key, v => v.Value.Aggregate((t, s) => (new List<string>(t.Union(s)))));

Answer 2

However are you trying to merge the values, you will probably want to use one of these options:

D3[1] = D1[1].Union(D2[1]);

or

D3[1] = D1[1].Concat(D2[1]);

Edit - an ugly-looking method for joined merges Linq-style:

foreach (var kvp in D1)
{
    D3[kvp.Key] =
        (from string letter in kvp.Value
        select
            (from IEnumerable<string> list in D2.Values
            where list.Contains(letter)
            select list)
             // Union all the D2 lists containing a letter from D1.
            .Aggregate((aggregated, next) => aggregated.Union(next)))
        // Union all the D2 lists containing all the letter from D1.
        .Aggregate((aggregated, next) => aggregated.Union(next))
        // Convert the unioned letters to a List.
        .ToList();
}

The code keeps the lists in D2, it would be pretty easy to modify the code to remove the matched lists from D2.