How do I push to Y axis at a given x index?

I want to push all the objects of one type into the y-axis at a given point. For example I want to push all arrows of type "artpiece" to x=0 and then y=0,1,2,... This works well for one row. But now I want to push all the values for the next type into x=1 and y=0,1,2...

So how can I specify at which x index to push into the y row?

When you push a new item the X is array.width-1 so you can use that to assign everything at x,y (array.width-1,y)