The timing is because A. (currently) doesn't "know" that it's being invoked with i.!n .
FYI, the Jwiki essay *Permutation Index <https://code.jsoftware.com/wiki/Essays/Permutation_Index> *describes how A. does its thing. A. is particularly amusing on large arguments. (_1+!30x) A. i.30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 A. |. i.30 265252859812191058636308479999999 !30x 265252859812191058636308480000000 On Mon, May 25, 2020 at 11:51 PM Jan-Pieter Jacobs < janpieter.jac...@gmail.com> wrote: > Yes, I just figured it out the same definition. > > However, I was very surprised to see perm massively outperforms tap: > > timespacex 'a=: perm 10' > 0.3946 3.18771e8 > timespacex 'b=: (A.&:i.~ !) 10' > 2.74118 5.62038e8 > a-:b > 1 > > JVERSION > Engine: j901/j32/android > Release-e: commercial/2020-02-09T15:23:16 > Library: 9.01.24 > J Android: 1.4.08/7.1.2/25 > Platform: Android 32 (armeabi-v7a) > Installer: unknown > InstallPath: /storage/emulated/0/Android/data/com.jsoftware.j.android/files > Contact: www.jsoftware.com > > > Perhaps an opportunity for performance improvement in dyadic A. ? > > Best regards, > > Jan-Pieter > > On Mon, May 25, 2020, 22:59 'Mike Day' via Programming < > programm...@jsoftware.com> wrote: > > > If I can’t remember the idiom, I look for “tap.” My favourite form is > > tap =: A.&i.~ ! > > > > (perm-: tap)3. NB. Same results..... > > 1 > > > > Cheers, > > > > Mike > > Sent from my iPad > > > > > On 25 May 2020, at 21:44, Skip Cave <s...@caveconsulting.com> wrote: > > > > > > perm > > > > > > 3 : 0 > > > > > > z=. i.1 0 > > > > > > for. i.y do. z=. ,/ (0 ,. 1 + z) {"2 1 \:"1 = i. 1 + {: $z end. > > > > > > : > > > > > > ,/ ({~ perm@#)"1 x comb y > > > > > > ) > > > > > > > > ---------------------------------------------------------------------- > > 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
