(rand-weighted ..args) args: two or more arguments (any type) returns any type
Randomly selects one item from a group, with unequal probability.
Expects an even number of arguments, where the even-numbered arguments are all non-negative numbers (weights). The sum of all weights must be greater than 0.
Each argument's likelihood of being chosen is equal to
(/ weight sum). For example,
(rand-weighted 'x 2 'y 3 'z 0) has a two-in-five chance of returning
'x and a
three-in-five chance of returning
'y. It will never return