http://www.jsoftware.com/jwiki/Essays/Power_Set
----- Original Message ----- From: Tracy Harms <[EMAIL PROTECTED]> Date: Sunday, June 8, 2008 12:25 Subject: [Jprogramming] from each To: [email protected] > Thank you, David and Raul, for those two solutions. Using > David's approach, the verb I was working on is complete. > It lists all subsets of an input list, a.k.a. all combinations > of all possible lengths between zero and totality. > > cc=: 3 : 0 > ty=. #y > zz=. <'' NB. same as <"_1 (0 comb ty) > for_h. >:i.ty do. zz=. zz , <"_1 h comb ty end. > zz {&.> <y > ) > > The verb comb (all combinations) is drawn from the J > Dictionary|Control Structures|For > http://www.jsoftware.com/help/dictionary/cfor.htm > as usual. > > The technique Raul proposed only works with literal and numeric > input. It's not a good fit here because I want this verb > to receive a list of boxes and produce results parallel to what > it produces with other data-types. (I don't yet understand the > niceties of why this is so.) > > If anybody thinks the for.-loop of this verb (cc) would be > neatly replaced by some other structure, I'd be interested in > hearing about it. > > Tracy ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
