NetLogo: excluding items from a list after they have already been chosen

I am using the setxy function to set the area that my turtles will be placed in. I made a list of the x values and y values. But I don't want more than 1 turtle at the same point. I'm not sure how to stop this from happening. This is the code that I am using for this: create-vcells 20 [ setxy one-of [0 0.6 1.2 1.8 2.4 3] one-of [0 0.6 1.2 1.8 2.4]

Does anyone have any insight? Thanks!