From: walter a kehowski <wkehowski@...>
Date: 2005-08-08T08:31:09+09:00
Subject: Re: cartesian product

Hello,

If one defines

class Array
  def cartprod(b)
    each do |ae|
      b.each do |be|
        if block_given?
          yield ae, be
        else
          (c ||= []) << [ae, be]
        end
      end
    end
    c
  end
end

then

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

c=cartpord(a.slice(0..-1))

c.each  {|ce| ce.each {|x| print x," " }; print "\n" }

gives the error

cartprod.rb:45: undefined method `cartpord' for main:Object (NoMethodError)

and

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

c=a[0]

b=a.slice(1..-1)

b.each{|be| c=c.cartprod(be) }

c.each  {|ce| ce.each {|x| print x," " }; print "\n" }

gives the error

cartprod.rb:24:in `cartprod': undefined local variable or method `c' for [1, 
2, 3]:Array (NameError)
        from cartprod.rb:49
        from cartprod.rb:49:in `each'
        from C:/Documents and Settings/walter/My Documents/cartprod.rb:49

and, finally,

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

c=cartprod(a)

c.each  {|ce| ce.each {|x| print x," " }; print "\n" }

gives the error

cartprod.rb:45: undefined method `cartprod' for main:Object (NoMethodError)

Well, I'm clearly plying around trying to get it JUST RIGHT.

Walter Kehowski