Get index of 2d array?

1

How can i obtain the index of a multidimensional array, preferably the first out of the two? (the 1,2,3. not 0):

*arrayThing[0][0].addEventListener(MouseEvent.CLICK, trace*Array);
*arrayThing[1][0].addEventListener(MouseEvent.CLICK, trace*Array);
*arrayThing[2][0].addEventListener(MouseEvent.CLICK, trace*Array);

*function traceArray(e:MouseEvent)
{
     trace(How do i obtain either 0,1, or 2, depending on which was clicked?);
}

*

thanks.