From: Martin DeMello <martindemello@...>
Date: 2005-08-08T17:01:08+09:00
Subject: Re: cartesian product

walter a kehowski <wkehowski@cox.net> wrote:
> 
> cartprod.rb:24: syntax error
>         (c ||= []) << ae,be
>                          ^
> cartprod.rb:26: syntax error
> cartprod.rb:132: syntax error

My mistake, sorry. Should be (c ||= []) << [ae, be]

> and I would like to take the cartesian product of an arbitrary number of 
> sets in the most elegant way.

Define a cartprod2 that takes the cartesian product of two arrays.
Define base cases sensibly - cartprod2([], a) = a.map {|i| [i]} and
cartprod2(a,b) = a.each {|i| b.each {|j| c << i.concat(j)}}

Use that as a helper function for cartprod thus:

def cartprod(*arrays)
  arrays.inject([]) {|prod, ary| cartprod2(prod, ary)}
end

Untested, but that's the general idea.

martin