ruby cookbook -- Choosing Randomly from a Weighted List

Recipe 5.11. Choosing Randomly from a Weighted List
Store the elements in a hash, mapped to their relative probabilities. The following code will work with a hash whose keys are mapped to relative integer probabilities:

def choose_weighted(weighted)
  sum = weighted.inject(0) do |sum, item_and_weight|
    sum += item_and_weight[1]
  end
  target = rand(sum)
  weighted.each do |item, weight|
    return item if target <= weight
    target -= weight
  end
end

很聪明的做法