Question

I have a list of Objects which are not comparable. I however would still like to sort this list of Objects based on a provided array of index positions. What is the fastest and most efficient way to sort this list? Here is an example:

List<Colour> list = new ArrayList<Colour>();
list.add(Colour.BLUE);
list.add(Colour.GREEN);
list.add(Colour.RED);
list.add(Colour.YELLOW);
list.add(Colour.GREEN);

int[] order = new int[] {3, 1, 2, 0, 4};

The final list should look like:

[YELLOW, GREEN, RED, BLUE, GREEN]

My specific requirement is for a solution in Java but I would be interested to know the solution in other languages as well.

Answer 1

Why don’t you just create the list from the indexes directly? No “sorting” is required.

List<Colour> sortedList = new ArrayList<Colour>();
for (int index : order) {
    sortedList.add(list.get(index));
}

Or C#:

var sorted = order.Select(index => list[index]).ToList();