From: Robert Klemme <shortcutter@...>
Date: 2006-01-16T18:34:39+09:00
Subject: Re: Generating combinations from multiple sets

In case the gateway is broken again:

I have a shorter alternative; it may be more efficient but you'll have to
test that for yourself:

def all_combinations(enum,&bl)
  pre = ""
  post = ""
  middle = []
  enum.each_with_index do |en,idx|
    item = "e#{idx}"
    pre << "enum[" << idx.to_s << "].each {|" << item << "| "
    middle << item
    post << "}"
  end
  eval(pre << "bl[" << middle.join(",") << "]" << post)
end

irb(main):053:0> all_combinations([[1,2,3],%w{a b c d}]) {|*a| p a}
[1, "a"]
[1, "b"]
[1, "c"]
[1, "d"]
[2, "a"]
[2, "b"]
[2, "c"]
[2, "d"]
[3, "a"]
[3, "b"]
[3, "c"]
[3, "d"]
=> [1, 2, 3]

You can even change this to work with arbitrary Enumerables - this version
depens on "enum" being an Array.

Kind regards

    robert