From: Pierre Barbier de Reuille <pierre.barbier@...>
Date: 2005-09-13T18:51:33+09:00
Subject: Re: possible bug?

Stefan Kaes a �crit :
> Hi,
> 
> I have a piece of code which I think should be working, but it doesn't.
> 
> def standard_dev(a, mean)
>   Math.sqrt((a.inject(0.0){|v,r| r += (v-mean)*(v-mean) })/a.length)
> end

Well, try this :
def standard_dev(a, mean)
  Math.sqrt((a.inject(0.0){|r,v| r += (v-mean)*(v-mean) })/a.length)
end

....

The doc says:

enum.inject {| memo, obj | block } => obj

You just swapped the two arguments ...

Pierre

> 
> computes results that don't make sense and differ from the values
> computed by this code:
> 
> def standard_dev(a, mean)
>   r = 0.0
>   a.each{|v| r += (v-mean)*(v-mean) }
>   Math.sqrt(r/a.length)
> end
> 
> I think the two should be different. Am I missing something?
> 
> -- stefan
> 
> 
>