how does one group notes in a 4/8 time?

for example i have: (q)=quaver, (s)=semiquaver, (d)=demisemi quaver

q s s d d d d s s | s s d d s q q ||

are the groupings in twos? so i would have


q-s-s d-d-d-d s-s | s-s-d-d s q-q ||


my book says that the groupings are 'slightly different'
but they don't actually explain how (¬_¬)

help + thanks!