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

Or how about:

class Stats
    def initialize( a )
        @avg = a.count > 0 ? a.sum / a.count.to_f : 0.0
        @stdev = a.count > 0 ? ( a.reduce(0){ |sum, v| sum + (@avg - v) ** 2 } / a.count ) ** 0.5 : 0.0
    end
end