enum math

e.rb

module Enumerable

  def sum
    self.reduce :+
  end
  
  def mean
    self.sum / self.size
  end
  
  def median
    self.sort[self.size / 2]
  end
  
  def variance
    average = self.mean
    self.reduce {|deviation_sum, value| deviation_sum + (value - average) ** 2} / self.size
  end

  def standard_deviation
    Math.sqrt self.variance
  end

end