From: MonkeeSage <MonkeeSage@...>
Date: 2007-12-16T19:05:02+09:00
Subject: Re: An idiomatic way to traverse all pairs in an enumerable?

On Dec 15, 6:25 pm, Rob Biedenharn <R...@AgileConsultingLLC.com>
wrote:
> On Dec 15, 2007, at 6:03 PM, Shot (Piotr Szotkowski) wrote:
>
>
>
> > I seem to end up doing the following quite a lot:
>
> > enum.each do |a|
> >  enum.each do |b|
> >    next if a >= b
> >    # do_something with a and b
> >  end
> > end
>
> > In general, I'm looking for an idiomatic way of traversing each
> > possible pair of a given enum's contents (once). Is there a more
> > compact construct?
>
> > (I assume I could finally grasp the whole block-passing side of Ruby
> > and write my own Enumerable#each_mix, but maybe there's something
> > there
> > already. Note: Enumerable#each_pair doesn't cut it, as it's just for
> > neighbouring element pairs, while I need something for all possible
> > pairs.)
>
> > Thanks in advance for any help with the above!
>
> > -- Shot
> > --
> > The existential root of libertarianism is the experience of
> > being very bad at taking orders from morons.   -- Leopold Leider
>
> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-list/42671
>
> You could use the Array#combination code posted there either directly
> or as an example.  If you can rely on the ordering of elements (your
> a>=b), your code isn't too bad, but the code on the ruby list will be
> (is) part of Ruby1.9 and only depends on position within the Array.
> If you have an enumerable that's not an Array, you might have some
> tweaking to do anyway.
>
> -Rob
>
> Rob Biedenharn          http://agileconsultingllc.com
> R...@AgileConsultingLLC.com

module Enumerable
  def every_pair(other)
    self.each { | x |
      other.each { | y |
        yield [x, y] if x < y
      }
    }
  end
end

a = [1, 8, 3]
b = [4, 5, 6]
a.every_pair(b) { | x, y |
  puts "doing stuff with " + [x, y].inspect
}
# =>
doing stuff with [1, 4]
doing stuff with [1, 5]
doing stuff with [1, 6]
doing stuff with [3, 4]
doing stuff with [3, 5]
doing stuff with [3, 6]

Regards,
Jordan