From: Xavier Noria <fxn@...>
Date: 2007-04-28T22:45:31+09:00
Subject: Re: cyclic array

On Apr 28, 2007, at 3:10 PM, Josselin wrote:

> I would like to print  n elements from an Array in a cyclic way.
>
> I mean :
>
> using anArray = [ "a", "b", "c", "d", "e", "f", "g"], I should do :
>
> anArray.print_cyclic(4, 0) => "a", "b", "c", "d"   (first print  4  
> elements starting with the first one)
>
> anArray.print_cyclic_next => "b", "c", "d", "e"
> anArray.print_cyclic_next => "c", "d", "e", "f"
> anArray.print_cyclic_next => "d", "e", "f", "g"
> anArray.print_cyclic_next => "e", "f", "g", "a"
> anArray.print_cyclic_next =>  "f", "g", "a", "b"
> anArray.print_cyclic_next => "g", "a", "b", "c"
> .....
> also in reverse cycle
> anArray.print_cyclic(4, 0) => "a", "b", "c", "d"
> anArray.print_cyclic_previous => "g", "a", "b", "c"
> anArray.print_cyclic_previous => "f", "g", "a", "b",
>
> what could be the simplest way to do it ?  no simple way using  
> Array class methods only  ,
> should I define a class and methods to loop into the array ?  any  
> existing lib ?  if it has been already done why should I rewrite  
> it ....


This is a possible approach:

   module Enumerable
     def each_cycle(window, start=0)
       (start...length+start).each do |i|
         yield((i..i+window).map {|n| self[n % length]})
       end
     end
   end

Usage is:

   a = [ "a", "b", "c", "d", "e", "f", "g"]
   a.each_cycle(4) do |cycle|
     puts "#{cycle}"
   end

You can delegate reverse cycle to each_cycle on the reverse (and  
perhaps taking the opposite of start mod length, depending on the  
meaning of start).

-- fxn