P.S. I am aware of the rshuffle command, which could potentially be useful for this problem (certainly easier than manually deciding an order for stimulus presentation!). However, as far as I understand rshuffle, you have to specify a set order for the categories you’re drawing from, so in my case I’d have to say present items in order e.g., B-A-C (wherein items from within each of those three groups are randomly selected). So category is not really randomly presented, but items are.