Good way to get the key of the highest value of a Dictionary in C#

Question

I'm trying to get the key of the maximum value in the Dictionary<string, double> results.

This is what I have so far:

double max = results.Max(kvp => kvp.Value);
return results.Where(kvp => kvp.Value == max).Select(kvp => kvp.Key).First();

However, since this seems a little inefficient, I was wondering whether there was a better way to do this.

Answer 1

This is a fast method. It is O(n), which is optimal. The only problem I see is that it iterates over the dictionary twice instead of just once.

You can do it iterating over the dictionary once by using MaxBy from morelinq.

results.MaxBy(kvp => kvp.Value).Key;

Answer 2

I think using the standard LINQ Libraries this is as fast as you can go.

Answer 3

Maybe this isn't a good use for LINQ. I see 2 full scans of the dictionary using the LINQ solution (1 to get the max, then another to find the kvp to return the string.

You could do it in 1 pass with an "old fashioned" foreach:

KeyValuePair<string, double> max = new KeyValuePair<string, double>(); 
foreach (var kvp in results)
{
  if (kvp.Value > max.Value)
    max = kvp;
}
return max.Key;

Answer 4

I think this is the most readable O(n) answer using standard LINQ.

var max = results.Aggregate((l, r) => l.Value > r.Value ? l : r).Key;