Given real usage statistics, build probabilities around choices and give me a random item

stochastic_hash.rb

class StochasticHash
  attr_accessor :data

  def initialize(data)
    @data = data
  end

  def total
    @total ||= data.values.sum
  end

  def build_ranges
    baseline = 0
    ret = {}

    data.each do |key, value|
      ret[(baseline..baseline+value)] = key
      baseline += value
    end

    return ret
  end

  def ranges
    @ranges ||= build_ranges
  end

  def pick
    number = rand(total)

    ranges.each do |range, solution|
      if range.include?(number)
        return solution
      end
    end

    # Fall back to just picking something
    return data.keys.sample
  end
end


# USAGE

quality_choices = StochasticHash.new({
  prime: 1_272_838,
  choice: 15_582_961,
  select: 3_925_873,
  standard: 596,
  commercial: 4_148,
  utility: 24_878,
  cutter: 0,
  cannery: 0
})

quality_choices.pick
=> :choice