Select random item with weight

Question

I have a list of approx. 10000 items. The current situation is that every item has an associated weight (priority or importance). Now the smallest weight is -100

Answer 1

It's easier to do if the weights are not negative. If you have to have negative weights, you'll have to offset the weights by the lowest possible weight. In your case, offsetted_weight = itemweight + 100

In pseudocode, it goes like this:

Calculate the sum of all the weights.
Do a random from 0 to the sum of the weights
Set i to 0
While the random number > 0
    Subtract the weight of the item at index i  from random
    If the random number is < 0 return item[i]
    Add 1 to i