Just a short remark - when I read your subject
"subtract arrays" I got a wrong idea what is your task about. Somehow I thought you need to find the difference between the two arrays in terms of elements which are in.
But it appears you need to subtract arrays elements one from another.
Be careful when choosing subject description or actual problem's description. It is important to get it right, otherwise you could get the advices which are not the ones you were expecting