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 results.

This is what I have so far:

double max          


        

Answer 1

My version based off the current Enumerable.Max implementation with an optional comparer:

    public static TSource MaxValue(this IEnumerable source, Func function, IComparer comparer = null)
    {
        comparer = comparer ?? Comparer.Default;
        if (source == null) throw new ArgumentNullException(nameof(source));

        TSource max = default;
        TConversionResult maxFx = default;
        if ( (object)maxFx == null) //nullable stuff
        {
            foreach (var x in source)
            {
                var fx = function(x);
                if (fx == null || (maxFx != null && comparer.Compare(fx, maxFx) <= 0)) continue;
                maxFx = fx;
                max = x;
            }
            return max;
        }

        //valuetypes
        var notFirst = false;
        foreach (var x in source) 
        {
            var fx = function(x);
            if (notFirst)
            {
                if (comparer.Compare(fx, maxFx) <= 0) continue;
                maxFx = fx;
                max = x;
            }
            else
            {
                maxFx = fx;
                max = x;
                notFirst = true;
            }
        }
        if (notFirst)
            return max;
        throw new InvalidOperationException("Sequence contains no elements");
    }

Example usage:

    class Wrapper
    {
        public int Value { get; set; }    
    }

    [TestMethod]
    public void TestMaxValue()
    {
        var dictionary = new Dictionary();
        for (var i = 0; i < 19; i++)
        {
            dictionary[$"s:{i}"] = new Wrapper{Value = (i % 10) * 10 } ;
        }

        var m = dictionary.Keys.MaxValue(x => dictionary[x].Value);
        Assert.AreEqual(m, "s:9");
    }