gistfile1.rb

  def self.cumulative_by_month model, column
    tally = 0
    count_by_month(model, column).map do |(month, count)|
      [month, tally += count]
    end
  end

  def self.cumulative_by_month_inject model, column
    count_by_month(model, column).tap {|pairs|
      pairs.inject(0) do |tally,pair|
        pair[1] = tally + pair[1]
      end
    }
  end