Obtain the index of the maximum element

Question

Given such a list:

        List intList = new List();
        intList.Add(5);
        intList.Add(10);
        intList.Add(15);
                


        

Answer 1

Here's a custom LINQ method which I believe does what you want. (I previously had another which does a projection, but you can just call Select to do that, as you only need the index.)

public static int MaxIndex<T>(this IEnumerable<T> source)
{
    IComparer<T> comparer = Comparer<T>.Default;
    using (var iterator = source.GetEnumerator())
    {
        if (!iterator.MoveNext())
        {
            throw new InvalidOperationException("Empty sequence");
        }
        int maxIndex = 0;
        T maxElement = iterator.Current;
        int index = 0;
        while (iterator.MoveNext())
        {
            index++;
            T element = iterator.Current;
            if (comparer.Compare(element, maxElement) > 0)
            {
                maxElement = element;
                maxIndex = index;
            }
        }
        return maxIndex;
    }
}

Answer 2

Use a custom function, using Max() and IndexOf() cost more.

Answer 3

public static class Extensions
{
    public static int MaxIndex<T>(this IEnumerable<T> TSource)
    {
        int i = -1;
        using (var iterator = TSource.GetEnumerator())
            while (iterator.MoveNext())
                i++;
        return i;
    }
}

Here is my crack at this problem. I returned -1 instead of throwing an exception because this is what the FindIndex function does and I find it very convenient.