From: Martin DeMello <martindemello@...>
Date: 2005-08-07T23:51:08+09:00
Subject: Re: cartesian product

Robert Klemme <bob.news@gmx.net> wrote:
> 
> Note that it might be more memory efficient to write a iteration method:
> 
> def cartprod(a,b)
>   a.each {|ae| b.each {|be| yield ae, be}}
> end
> 
> Then you can also do this if needed
> 
> c=[]
> cartprod(a,b) {|x,y| c << [x,y]}
> 
> If you just need every combination once the iteration approach is more 
> efficient.

Or even better, 

if block_given?
  yield ae, be
else
  (c ||= []) << ae, be
end

martin