gistfile1.rbx

class Array

  def weighted_random(weight_method=:weight)
    return nil if empty?                       # return nil if there's no elements
    elements = sort_by { Kernel.rand }         # shuffle the elements.
    weights = elements.map(&weight_method)     # get the weight for each element (e.g.: 5, 10, 2, 0, 1, 5).
    point = Kernel.rand * weights.sum          # pick a random point between zero and the sum of the weights.
    elements.zip(weights).each do |e, weight|  # walk through each element,
      return e if weight >= point              #   and if its weight is >= the point, return it
      point -= weight                          #   otherwise subtract the element's weight from the point
    end
  end
  
end