On closer inspection, f^:v^:n doesn’t seem to work (as I want it to). What it does is to skip evaluation each time v y returns 0. While this would work in my situation, as the stopping condition would remain true, it would of course be unnecessary (and inefficient) to keep checking this for the remainder of the iterations.
Thanks, Anton Wallgren On 26 May 2020, 10:17 +0200, Anton Wallgren <[email protected]>, wrote: > Yes, probably something wrong with my stop-function (rank perhaps?). When I > run > > (f^:(0.8"_ > ?@0:)^:5) y > > (replacing the stop function with a random function), everything seems to > work fine. > > It seems like this functionality is something that could easily be added to > Z: though, since _3 Z: n aborts execution without producing a return value > after n iterations. But maybe the functionality is, as you say, quirky :). > I’m into metaheuristic search, where this kind of pattern is not uncommon > (try to find good solutions for a fixed set of iterations and/or time, but > stop early if a good enough solution is found). > > Regards, Anton Wallgren > On 26 May 2020, 10:02 +0200, Anton Wallgren <[email protected]>, wrote: > > Yes, maybe for loop is the way to go. It just seems very un-J :). I did try > > f^:v^:n earlier, but it didn’t work, it ran f 2*n times. But when I try it > > now with my simple example, > > > > (2&*)^:(10&> @ ])^:3 ] 1 > > > > returns 8, and > > > > (2&*)^:(10&> @ ])^:5 ] 1 > > > > returns 16, as expected. Maybe there is something going on with my “v” in > > my earlier code. > > > > Thanks, Anton Wallgren > > On 26 May 2020, 09:11 +0200, Raul Miller <[email protected]>, wrote: > > > ^:_ doesn't impose the max limit on iterations, though... > > > > > > I think, for something that quirky, I'd just use a for loop. That > > > said, f^:v^:n would work -- I'm just not sure it's optimized > > > adequately. > > > > > > I hope this helps, > > > > > > -- > > > Raul > > > > > > On Tue, May 26, 2020 at 2:39 AM 'Rob Hodgkinson' via Programming > > > <[email protected]> wrote: > > > > > > > > Hi Anton, welcome to J. > > > > > > > > This is a further parameter to the power operator (^:) described here: > > > > > > > > https://code.jsoftware.com/wiki/Vocabulary/Loopless > > > > <https://code.jsoftware.com/wiki/Vocabulary/Loopless> Section “Types of > > > > Loops” and the row in the table “Apply a verb repeatedly”, “Until a > > > > condition is met”. > > > > Use Power ([x] u^:v^:_ y) > > > > > > > > For your example, double while a condition (eg let’s say while the > > > > sequence is < 100 and stop with the value that breaches that condition > > > > …) > > > > > > > > 2&* ^:(100>])^:_ (1) NB. Sequence here is 1,2,4,8,16,32,64,128 > > > > 128 > > > > > > > > 2&* ^:(100>])^:_ (5) NB. Sequence is 5, 10, 20, 40, 80, 160 > > > > 160 > > > > > > > > Best, Rob > > > > > > > > > On 26 May 2020, at 4:09 pm, Anton Wallgren <[email protected]> > > > > > wrote: > > > > > > > > > > Hello! > > > > > > > > > > Fairly recent J enthusiast here. I’m wondering about the idiomatic > > > > > way to iterate at most n times? I.e. do f^:n y, but with the > > > > > possibility of an early exit if some condition is met. Is it (u F. ]) > > > > > y, where u is f but with some Z:’s added? E.g > > > > > > > > > > f=: 2&* > > > > > MAX=: n > > > > > > > > > > u=: monad define > > > > > _2 Z: -.*MAX=: MAX - 1 > > > > > _2 Z: some other condition > > > > > f y > > > > > ) > > > > > > > > > > But then you need to globally assign and reassign MAX and this > > > > > doesn’t feel very elegant. Another option of course is to use a > > > > > for-loop with break. > > > > > > > > > > Thanks, Anton Wallgren > > > > > ---------------------------------------------------------------------- > > > > > 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 > > ---------------------------------------------------------------------- > > 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
