I think there is a weighted expression, you might need to convert the data type but for examples you can use

.RandomChoiceWeighted("1,2,3,4,5,6,7,8,9,10", "1,1,1,1,1,2,2,2,3,3")

this will pick a number between 1 and 10
with 9,10 being 3x more likely to be chosen
6,7,8 being 2x more likely to be chosen
and 1,2,3,4,5 being the least likely to be chosen

if this is not what you are looking for let me know more details about exactly what your looking and I can add something for it.