Question

okay, I have a list of class objects like so:

List<fruit> lst = new List<fruit>();
    lst.Add(orange);
    lst.Add(apple);
    lst.Add(grape);
    lst.Add(grape);
    lst.Add(orange);
    lst.Add(pear);
    lst.Add(apple);

I want to be able to ask the list something like
GetIndex(“orange”, 2) and have it return (in this case) the index # for the second instance of object in question (position 4).

This list will be dynamically filled, and it may not even have an orange to begin with. If it does, I want the instance number of the second parameter. So I can get the second orange, or get fifth mango, etc.

list.IndexOf(orange) returns the first instance of any duplicates, so I need something else.

Any ideas?

PS: I failed to mention that the first param will be a string!

Answer 1

You can extend classes with your own method for that class, sadly this is not possible for generic classes, so instead you give the type with the method.

public static class ListExtension
{
    public static int GetIndex<T>(this List<T> list, T value, int skipMatches = 1)
    {
        for (int i = 0; i < list.Count; i++)
            if (list[i].Equals(value))
            {
                skipMatches--;
                if (skipMatches == 0)
                    return i;
            }
        return -1;
    }
}

List<int> list = new List<int>();
list.Add(3);
list.Add(4);
list.Add(5);
list.Add(4);
int secondFour = (int)list.GetIndex(4, 2);