Loop into a dictionary and switch to the index

Considering this dictionary :

let dict = [("Steve", 17),
             ("Marc", 38),
             ("Xavier", 21),
             ("Rolf", 45),
             ("Peter", 67),
             ("Nassim", 87),
             ("Raj", 266),
             ("Paul", 220),
             ("Bill", 392)]

Howt to loop through it and switch to the index in order to make operations with the three first, the three next and the last three.