WeightedSampler -> Randoms with weight

gistfile1.rb

class WeightedSampler
  def initialize(items)
    @items = normalize(items)
  end

  def sample(num = nil)
    return get_sample unless num
    Array.new(num) { get_sample }
  end

  private

  def get_sample
    pick = rand()
    @items.each do |key, weight|
      return key if pick <= weight
      pick -= weight
    end
    nil
  end

  def normalize(items)
    sum = items.values.inject(0.0, :+)
    items.each_with_object({}) do |(key, weight), memo|
      memo[key] = weight / sum
    end
  end
end