How can I do standard deviation in Ruby?

Question

I have several records with a given attribute, and I want to find the standard deviation.

How do I do that?

Answer 1

As a simple function, given a list of numbers:

def standard_deviation(list)
  mean = list.inject(:+) / list.length.to_f
  var_sum = list.map{|n| (n-mean)**2}.inject(:+).to_f
  sample_variance = var_sum / (list.length - 1)
  Math.sqrt(sample_variance)
end