Perhaps something like this: http://jsfiddle.net/QFzCY/
var blocksPerRow = 4;
$("body").on("keydown", function(e){
var thisIndex = $(".selected").index();
var newIndex = null;
if(e.keyCode === 38) {
// up
newIndex = thisIndex - blocksPerRow;
}
else if(e.keyCode === 40) {
// down
newIndex = thisIndex + blocksPerRow;
}
if(newIndex !== null) {
$(".test").eq(newIndex).addClass("selected").siblings().removeClass("selected");
}
});
Basically, you set how many items there are in a row and then find the current index and subtract or add that amount to select the next element via the new index.
If you need to know how many blocks per row there are, you could do this:
var offset = null;
var blocksPerRow = 0;
$(".test").each(function(){
if(offset === null) {
offset = $(this).offset().top;
}
else if($(this).offset().top !== offset) {
return false;
}
blocksPerRow++;
});
To deal with your 'edge' cases, you could do:
if(newIndex >= $(".test").length) {
newIndex = $(".test").length - newIndex;
}