Generic List - moving an item within the list

Question

So I have a generic list, and an oldIndex and a newIndex value.

I want to move the item at oldIndex, to newIndex...as simply as possible.

Any suggestions?

Note

The item should be end up between the items at (newIndex - 1) and newIndex before it was removed.

Answer 1

I would expect either:

// Makes sure item is at newIndex after the operation
T item = list[oldIndex];
list.RemoveAt(oldIndex);
list.Insert(newIndex, item);

... or:

// Makes sure relative ordering of newIndex is preserved after the operation, 
// meaning that the item may actually be inserted at newIndex - 1 
T item = list[oldIndex];
list.RemoveAt(oldIndex);
newIndex = (newIndex > oldIndex ? newIndex - 1, newIndex)
list.Insert(newIndex, item);

... would do the trick, but I don't have VS on this machine to check.

Answer 2

var item = list[oldIndex];

list.RemoveAt(oldIndex);

if (newIndex > oldIndex) newIndex--; 
// the actual index could have shifted due to the removal

list.Insert(newIndex, item);

Answer 3

Something like this:

List<object> l;
l.Insert(newIndex, l[oldIndex]);
if(newIndex <= oldIndex) ++oldIndex;
l.RemoveAt(oldIndex);

EDIT: Taking in to account the index shift, hope its correct. (tks for the comments)

Answer 4

List<T>.Remove() and List<T>.RemoveAt() do not return the item that is being removed.

Therefore you have to use this:

var item = list[oldIndex];
list.RemoveAt(oldIndex);
list.Insert(newIndex, item);

Answer 5

Simplest way:

list[newIndex] = list[oldIndex];
list.RemoveAt(oldIndex);

EDIT

The question isn't very clear ... Since we don't care where the list[newIndex] item goes I think the simplest way of doing this is as follows (with or without an extension method):

    public static void Move<T>(this List<T> list, int oldIndex, int newIndex)
    {
        T aux = list[newIndex];
        list[newIndex] = list[oldIndex];
        list[oldIndex] = aux;
    }

This solution is the fastest because it doesn't involve list insertions/removals.