From: walter a kehowski <wkehowski@...>
Date: 2005-08-11T20:06:11+09:00
Subject: cartesian product - next to last version

Hello,

Since the original thread got a little long, I decided to post my next to 
last version in a new thread. My previous version gave results like 
[[1,4],7] for more than two arrays when you really wanted [1,4,7]. The trick 
is to flatten each element of the product. The following works for any 
number of arrays. Of course you might want a product in which the elements 
of that product are arrays. Any suggestions?

class Array

  def cartprod(b=[])
    if b.empty? then
      #assume self an array of arrays
      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


a=[1,2,3]
b=[4,5,6]
c=[7,8,9]

# works fine
p [a,b,c].cartprod

# doesn't work since [1,4,7,[10,11]] is [1,4,7,10,11]
d=[10, [11,12]]
p [a,b,c,d].cartprod