Question

If I create a Comparer<T> for the purposes of sorting a set of objects, is there a simple way to ‘invert’ it so I can sort in the other direction? Or do I need to define a 2nd Comparer<T> with the tests in the Compare method swapped around?

Answer 1

public class ReverseComparer<T> : Comparer<T>
{
    private Comparer<T> inputComparer;
    public ReverseComparer(Comparer<T> inputComparer)
    {
        this.inputComparer = inputComparer;
    }

    public override int Compare(T x, T y)
    {
        return inputComparer.Compare(y, x);
    }
}

This allows you to do something like:

list.Sort(new ReverseComparer(someOtherComparer));