From: Carlos <angus@...>
Date: 2004-03-13T04:37:53+09:00
Subject: Re: iterating with multiple values

[gabriele renzi <surrender_it@rc1.vip.ukl.yahoo.com>, 2004-03-12 19.09 CET]
> Hi gurus and nubys,
> 
> Suppose you are dealing with an array like [1,2,3,4], and suppose ypou
> want to deal, at any iteration, with 3 values.I mean something like:
> 
> [1,2,3,4].each_3 do |pre,cur,next|
>  print pre,cur,next,"\n"
> end
> 
> nil,nil,1
> nil,1,2
> 1,2,3
> 2,3,4
> 3,4,nil
> 4,nil,nil
> 
> What do you think is the best way to this? I can think of adding a
> global index and use it to refer explicitly to an element oin the
> array, but this is ugly to me.. 
[...]

You can use an array to buffer intermediate results. Something like
(not tested):

module Enumerable
  def each_n(n)
     a = Array.new(n)
     each do |cur|
         a.shift
         a.push cur
         yield *a
     end
     (a.size-1).times do
         a.shift
         a.push nil
         yield *a
     end
  end
end

Good luck.