我如何在Ruby中做标准偏差？

def mean(array)
  array.sum / array.length.to_f
end

def variance(array)
  m = mean(array)
  sum = array.inject(0) { |accum, i| accum + (i - m)**2 }
  sum / array.length.to_f
end

def standard_deviation(array)
  Math.sqrt(variance(array))
end

array = [1, 2, 3, 4, 5]
std_dev = standard_deviation(array)
puts "标准偏差: #{std_dev}"