From: Joel VanderWerf <vjoel@...>
Date: 2004-03-14T05:01:42+09:00
Subject: Re: iterating with multiple values

gabriele renzi wrote:
> 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

The enum tools library[1] has some methods for doing this:

   require 'enum/cluster'

   (0..5).each_with_neighbors { |x| p x }

   # prints:
   # [nil, 0, 1]
   # [0, 1, 2]
   # [1, 2, 3]
   # [2, 3, 4]
   # [3, 4, 5]
   # [4, 5, nil]

   [1,2,3,4].each_with_neighbors(8, 0) { |x| p x }

   # prints:
   # [0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 0, 0, 0, 0, 0]
   # [0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 0, 0, 0, 0, 0, 0]
   # [0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 0, 0, 0, 0, 0, 0, 0]
   # [0, 0, 0, 0, 0, 1, 2, 3, 4, 0, 0, 0, 0, 0, 0, 0, 0]

   ('a'..'g').each_cluster(5) { |x| p x.join '' }

   # prints:
   # "abcde"
   # "bcdef"
   # "cdefg"


[1] http://raa.ruby-lang.org/list.rhtml?name=enum