rolling_average.rb

module Enumerable
  def rolling_average(n)
    return enum_for(__method__, n) unless block_given?
  
    enum   = each
    values = n.times.map { enum.next } # rescue StopIteration
    sum    = values.inject(:+)
    yield sum.quo(n)
    loop do
      sum -= values.shift
      values << enum.next
      sum += values.last
  
      yield sum.quo(n)
    end
  end
end