Pick items from list with probability based upon property of list member ?

[southof40]

I have list of of N Vehicle objects - the only possible vehicles are
cars, bikes, trucks.

I want to select an object from the list with a probability of : cars
0.7, bikes 0.3, trucks 0.1.

I've currently implemented this by creating another list in which each
car object from the original list appears 7 times, each bike 3 times
and each truck once. I then pick at random from that list.

This works but seems very clunky to me. Can anyone suggest a better
data structure which would support the 'weighted randomness' I'm
after ?

I'm not fixed on the idea of using a list - could be a dictionary,
tree whatever .

Thanks in advance.

R.