Add :mean to Arrays

mean.rb

module WhiteHat101
  module Mean
    def mean
      inject(0.0, :+) / length
    end
    alias avg mean
    alias average mean
    
    def mean_absolute_deviation
      mean = self.mean
      map {|r| (mean - r).abs }.mean
    end
    alias mad mean_absolute_deviation
    
    def standard_deviation
      mean = self.mean
      Math.sqrt inject(0.0) {|sum, x| sum + (x - mean)**2 } / self.length.to_f
    end
    def standard_deviation2
      mean = self.mean
      Math.sqrt inject(0.0) {|sum, x| sum + (x - mean)**2 } / (self.length.to_f - 1)
    end
  end
end

Array.send :include, WhiteHat101::Mean

def eulers_method x0, y0, xN, step = 1.0, &block
  until x0 > xN
    puts "A(#{x0}) = #{y0} (step #{step})"
    y0 += step * block.call(x0, y0)
    x0 += step
  end
end

def dilate origin_x, origin_y, scale=1.0
  proc do |x,y|
    [origin_x+scale*(x-origin_x), origin_y+scale*(y-origin_y)]
  end
end
# [[2,2],[6,2],[2,5]].map &dilate(6,5,3) # => [[-6, -4], [6, -4], [-6, 5]]

Reflect over y = -x + 3

[[-2,5],[3,8],[2,6],[7,4],[7,2]].map{|x,y|[-y+3,-x+3]} # => [[-2, 5], [-5, 0], [-3, 1], [-1, -4], [1, -4]]