From: walter a kehowski <wkehowski@...>
Date: 2005-08-12T03:21:10+09:00
Subject: Re: cartesian product - next to last version

>
> In such cases, I use the Vector class (require 'matrix') as the
> 'atomic' unit. Then Array#flatten doesn't peek inside the Vectors and
> flatten them inappropriately.
>

require 'matrix'
# see page 694 of PR
#

class Array

  def cartprod(b=[])

    if b.empty? then
      #assume self an array of arrays
      z=inject {|cp,x| cp.cartprod(x) }
    else
      z = inject([]) {|a,x| b.inject(a) {|a,y| a << [x,y]}}
      z.collect! {|x| x.flatten }
    end
  end

end

#Everything works
a=[1,2]
b=[4,5]
c=[7,8]
p [a,b,c].cartprod

d=[10, Vector[11,12]]
p [a,b,c,d].cartprod