Question

I have this very simple array which I want to be able to move around some items in. Are there any built in tools in c# to do this? If not, du you have any suggestion in how to do it.

In example

var smallArray = new string[4];
smallArray[0] = "a";
smallArray[1] = "b";
smallArray[2] = "c";
smallArray[3] = "d";

And lets say I want to (programmatically) swap index 2 and 0, creating

smallArray[0] = "c";
smallArray[1] = "a";
smallArray[2] = "b";
smallArray[3] = "d";

Thanks.

Answer 1

EDIT: Okay, now you’ve changed the example, there’s nothing built-in – and it would actually be a bit of a pain to write… you’d need to consider cases where you’re moving it “up” and where you’re moving it “down”, for example. You’d want unit tests, but I think this should do it…

public void ShiftElement<T>(this T[] array, int oldIndex, int newIndex)
{
    // TODO: Argument validation
    if (oldIndex == newIndex)
    {
        return; // No-op
    }
    T tmp = array[oldIndex];
    if (newIndex < oldIndex) 
    {
        // Need to move part of the array "up" to make room
        Array.Copy(array, newIndex, array, newIndex + 1, oldIndex - newIndex);
    }
    else
    {
        // Need to move part of the array "down" to fill the gap
        Array.Copy(array, oldIndex + 1, array, oldIndex, newIndex - oldIndex);
    }
    array[newIndex] = tmp;
}

You should probably consider using a List<T> instead of an array, which allows you to insert and remove at particular indexes. Those two operations will be more expensive than only copying the relevant section, but it’ll be a lot more readable.