finding the max of value for each key in multiple dictionaries

Question

I have 3 dictionaries and need to create a new dictionary which should contain the highest number of value for the same key. For example r1 has (10, 100), r2 has (10, 200), r3 has (10, 500). The new dictionary should have 10, 500.

public Dictionary<Double, Double> r1 = new Dictionary<Double, Double>(); 
public Dictionary<Double, Double> r2 = new Dictionary<Double, Double>(); 
public Dictionary<Double, Double> r3 = new Dictionary<Double, Double>(); 

Answer 1

new[] { r1, r2, r3 }.SelectMany(p => p).GroupBy(p => p.Key)
                    .ToDictionary(g => g.Key, g => g.Max(p => p.Value));

Edit:

class Program
{
    static void Main()
    {
        var r1 = new Dictionary<double, double> { { 10, 200 } };
        var r2 = new Dictionary<double, double> { { 10, 300 } };
        var r3 = new Dictionary<double, double> { { 10, 500 } };

        var r = Merge(r1, r2, r3);

        foreach (var p in r)
            Console.WriteLine("{0}: {1}", p.Key, p.Value);
    }

    static IDictionary<double, double> Merge(params Dictionary<double, double>[] dicts)
    {
        return dicts.SelectMany(p => p).ToLookup(p => p.Key, p => p.Value).ToDictionary(p => p.Key, p => p.Max());
    }
}

Answer 2

Maybe something like this:

r1.Concat(r2).Concat(r3)
  .GroupBy(p => p.Key)
  .Select(g => new KeyValuePair<double, double>(g.Key, g.Max(p => p.Value)))
  .ToDictionary(p => p.Key, p  => p.Value);

Not tested but the idea is:

• get all the pairs
• group them by key
• generate a new pair with the max of each group
• convert this set to a dictionary