From: jogloran <jogloran@...>
Date: 2006-08-02T20:03:18+09:00
Subject: Re: Scientific calculation: get Std.Dev for a integer array

class Array
  def sd(ar)
    n = length
    sum_sq = inject(0.0) {|accu, v| accu + v*v}
    sum = inject(0.0) {|accu, v| accu + v}

    Math.sqrt((sum_sq - sum*sum/n) / (n-1))
  end
end

On 8/2/06, Sander Land <sander.land@gmail.com> wrote:
> On 8/2/06, Wang Austin-W22255 <xuwang@motorola.com> wrote:
> > Hi Ruby Gurus,
> >
> > Could you please point me how to do some scientific calculation in Ruby:
> >
> > 1) How to calculate std.dev for an integer array?
> > 2) Is there a log() function in Ruby?
> >
> > Thank you!
> > Austin
>
> 1) I don't think there's a builtin function for that, so you'll have
> to create your own.
> You'll probably want to add it to the Array class.
> class Array
>   def stddev
>     # your function here
>   end
> end
>
> You could also check rubyforge.org, maybe there's a statistics library
> available there.
>
> 2) Math.log
>
>