From: Trans <transfire@...>
Date: 2007-01-30T05:11:56+09:00
Subject: Re: cartesian product of arrays



On Jan 29, 10:09 am, "Trans" <transf...@gmail.com> wrote:
> On Jan 26, 6:05 am, Thomas Hafner <tho...@hafner.NL.EU.ORG> wrote:
>
>
>
> > Hello,
>
> > did I miss some standard library function? Anyway, then I'll do it on
> > my own:
>
> > def cartprod(*args)
> >   result = [[]]
> >   while [] != args
> >     t, result = result, []
> >     b, *args = args
> >     t.each do |a|
> >       b.each do |n|
> >         result << a + [n]
> >       end
> >     end
> >   end
> >   result
> > end
>
> > Example:
> > cartprod([1,2],[3,4,5],[6,7,8])
> > => [[1, 3, 6], [1, 3, 7], [1, 3, 8], [1, 4, 6], [1, 4, 7], [1, 4, 8],
> >     [1, 5, 6], [1, 5, 7], [1, 5, 8], [2, 3, 6], [2, 3, 7], [2, 3, 8],
> >     [2, 4, 6], [2, 4, 7], [2, 4, 8], [2, 5, 6], [2, 5, 7], [2, 5, 8]]Hi--
>
> I was going to say that Facets has cross:
>
>   require 'facets/core/enumerable/cross'
>
>   Enumerable.cross([1,2],[3,4,5],[6,7,8])
>   => [[1, 3, 6], [1, 3, 7], [1, 3, 8], [1, 4, 6], [1, 4, 7], [1, 4,
> 8], [1, 5, 6], [1, 5, 7], [1, 5, 8], [2, 3, 6], [2, 3, 7], [2, 3, 8],
> [2, 4, 6], [2, 4, 7], [2, 4, 8], [2, 5, 6], [2, 5, 7], [2, 5, 8]]
>
> Also when just deailing with a pair:
>
>   require 'facets/core/enumerable/op_pow'
>
>   [1,2] ** [3,4,5]
>   => [[1, 3], [1, 4], [1, 5], [2, 3], [2, 4], [2, 5]]
>
> there are two considerations though: 1) your implementation retains an
> additional array level for each initial possibility. is that desired
> behavior?

ignore that one, the layout of the result confused me.

T.