From: James Edward Gray II <james@...>
Date: 2007-04-09T23:16:52+09:00
Subject: Re: Creating an array of differences

On Apr 9, 2007, at 8:46 AM, Jason Madigan wrote:

> Hey there,

Hello.

> I'm pretty new to Ruby so perhaps some of you could help me out with a
> little problem I've come up against.

Sure.  Welcome to Ruby.

> 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"]).

Hmm, your description and your example don't say the same thing.   
I'll assume you meant the answer should be ["100", "100"].

> I'm not entirely sure how to go about this, so any pointers
> would be welcome.

With just core Ruby you could do:

 >> data = %w[1000 1100 1200]
=> ["1000", "1100", "1200"]
 >> (1..(data.size - 1)).inject(Array.new) do |diffs, i|
?>   diffs + [(data[i - 1].to_i - data[i].to_i).abs.to_s]
 >> end
=> ["100", "100"]

However, I think it looks a little prettier if you load a standard  
library and solve it like this:

 >> require "enumerator"
=> true
 >> data.enum_cons(2).map { |l, r| (l.to_i - r.to_i).abs.to_s }
=> ["100", "100"]

Hope that helps.

James Edward Gray II