This problem was solved earlier this year. I retained this solution from Arie Groeneveld but there were many others. It works with numbers and characters.
vari =: 4 :'y,/@:(],"1 0 -."1)^:(x-1) ,.y' 2 vari 'abc' ab ac ba bc ca cb #4 vari 1 3 4 6 8 9 360 On Tue, Nov 7, 2017 at 7:07 PM, 'Mike Day' via Programming < [email protected]> wrote: > That number is 360, ie > (!4) * 4!6 > as reported on that Quora example’s link. > > The comb verbs return the number of combinations, not of permutations. > > Cheers, > > Mike > > > Please reply to [email protected]. > Sent from my iPad > > > On 7 Nov 2017, at 22:26, 'Skip Cave' via Programming < > [email protected]> wrote: > > > > How many four digit numbers can be formed from the number 1,3,4,6,8 and > 9 if > > repetition of digits is not allowed? > > <https://www.quora.com/How-many-four-digit-numbers-can- > be-formed-from-the-number-1-3-4-6-8-and-9-if-repetition-of- > digits-is-not-allowed> > > > > Using Erling's CombE: > > > > b =. 4 CombE 6 > > > > a =. 1 3 4 6 8 9 > > > > #c = b#a > > > > 15 NB. so the answer is 15. > > > > NB. Convert to decimal > > > > 10 10 10 10#. c > > > > 1346 1348 1349 1368 1369 1389 1468 1469 1489 1689 3468 3469 3489 3689 > 4689 > > > > > > Wait a minute! > > > > What happened to 1364, 1384, 1396, 1436, 1438, 1439, and lots more? > > > > I was hoping CombE would give all combinations of y items taken x at a > time > > > > > > Skip > > > > > > > > > >> > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
