From: Rick DeNatale <rick.denatale@...>
Date: 2007-04-09T23:38:46+09:00
Subject: Re: Creating an array of differences

On 4/9/07, Jason Madigan <nuphor@gmail.com> wrote:
> Hey there,
>
> I'm pretty new to Ruby so perhaps some of you could help me out with a
> little problem I've come up against. I have an array consisting of
> integers (called session[:octets_in]). What I want to do is create an
> array comprising of the difference between the current element and the
> previous element (e.g. ["1000", "1100", "1200"] would become ["100",
> "200"]). I'm not entirely sure how to go about this, so any pointers
> would be welcome.

Did you really mean that this would produce ["100", "100"]? since the
element before "1200" is "1100" not "1000".

require 'enumerator'

["1000", "1100",  "1200", "1420"].enum_for(:each_cons, 2).map {|a, b|
(b.to_i - a.to_i).to_s} => ["100", "100", "220"]

If you really meant the difference between the second and subsequent
elements and the first, then here's a tricksy way to to it:

["1000", "1100",  "1200"].inject(nil) {|s,e| s ? s << (e.to_i -
s.first.to_i).to_s : [e]}[1..-1]

It stores the first element in the 'sum' being computed by inject,
then strips it off.
-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/