Little bit of array math

1

I need to pick each time one item from an array (only 4 items in an array)
but I need not to repeat last pick, (just last pick), so it can go “top”, “left”, “top”…
just not “top”, “top”…

var caseArr:Array = [ “top”, “left”, “bottom”, “right” ];
var r:int = Math.floor(Math.random() * caseArr.length);
_case = caseArr[r];