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MathGroup Archive 1997

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Cartesian product of n sets of lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg5860] Cartesian product of n sets of lists
  • From: Jean-Christophe Deschamps <jchd at worldnet.fr>
  • Date: Sun, 2 Feb 1997 01:30:35 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

PLEASE: be kind to mail answers to <jchd at worldnet.fr> as well.
I do _not_ receive this list at all here (I wonder why, since I got the
welcome automated message) and the feed for the Mma newsgroup is utterly
unreliable at this end, sigh!  Sorry for that unconvenience.


Using Mma v2.x, I never found the proper way to get the cartesian
product of several sets whose elements are themselves Lists.

In other terms, I would like to write something like this (using List as
operator):

p =3D CartProd[List, { {a, b, c}, {1, 2, 3} },
                   { {d, e, f}, {4, 5, 6} }]

and obtain four matrices:

  a b c     a b c     d e f     d e f
  1 2 3     4 5 6     1 2 3     4 5 6


Outer is of little use since it acts beyond level 1 of its arguments, e.g=
.:

Outer[List, { {a, b}, {1, 2} },
            { {c, d}, {3, 4} }]

{{{{{a, c}, {a, d}}, {{a, 3}, {a, 4}}}, {{{b, c}, {b, d}}, {{b, 3}, {b,
4}}}},=20
 {{{{1, c}, {1, d}}, {{1, 3}, {1, 4}}}, {{{2, c}, {2, d}}, {{2, 3}, {2,
4}}}}}


Of course, it's possible to define a bunch of functions (one taking 2
sets, one taking 3 sets, ...) like:

CartProd[f_, s1_List, S2_List] :=3D Block[{ii,jj},
  Flatten[ Table[ f[s1[[ii]], s2[[jj]] ],
                  {ii,Length[s1]}, {jj,Length[s2]} ], 1]]

but I find it a little ugly.


Thank you for your hints.
--
   jchd at worldnet.fr         | Jean-Chistophe Deschamps
                            |     14, rue Hermel
 T=E9l.: (33) 01 42 55 01 93  |      75018 Paris



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