Cool! Seems preferable to the for loop (at least for one example) as well
(modified a bit since I’m using a boxed array as y):
repuntil=: 2 : '((<:&.>@{. , u@}.) ` ] @. v)^:(0 < >@{.)^:_'
repuntil2=: 2 : 'for. i.x do. if. v y do. break. else. y=. u y end. end.'
cond=: 6 >: >@{:
depth=: 100000
timespacex '(search repuntil cond)"1 (< depth) ,"1 m'
38.0857 182080
timespacex 'depth (search repuntil2 cond)"1 m'
38.1578 1.2073e6
Regards, Anton Wallgren
On 26 May 2020, 13:45 +0200, Jan-Pieter Jacobs <[email protected]>,
wrote:
> Hi, I would do something like this:
>
> f=: +:
> cond=: 100<{:
> repuntil =: 2 : '((<:@{. , u@}.)`] @. v )^:(0<{.)^:_'
> f repuntil cond 20 1
> 0 32
>
> f repuntil cond 20 1
> 13 128
>
> the first item tells you whether:
>
> - if 0: iterations ended due to hitting the limit (first item of argument);
> or
>
> - if > 0, the condition became true.
>
> The agenda (@.) construct is just a way of making the left verb argument to
> the left-most ^: return the same twice, which triggers the end of the
> iteration by ^: _ .
>
> Good luck exploring J, it'll keep being interesting for long ;).
>
> Best regards,
>
> Jan-Pieter
>
> On Tue, May 26, 2020, 12:04 'Rob Hodgkinson' via Programming <
> [email protected]> wrote:
>
> > I don’t agree, it does not proceed further.
> >
> > ([x] u^:v^:_ y) will actually stop when v returns 0 (does not skip or
> > continue executing)
> >
> > Here is a simple way to confirm this using a function f to do 2&* but
> > which also uses ’smoutput’ to output to the session log (print intermediate
> > results).
> >
> > f=: verb define
> > smoutput r=:2*y
> > r
> > )
> >
> > f 5
> > 10 NB. Intermediate print using smoutput
> > 10. NB. Result of f
> >
> > Test it…
> > a=:f 5
> > 5. NB. It still prints within f via smoutput
> >
> > So now …
> > f^:(10>])^:3 ] 1
> > 2 }
> > 4 } Intermediates from smoutpout (f called 3 times)
> > 8 }
> > 8 NB. Result returned (ran to completion)
> > f^:(10>])^:4 ] 1
> > 2 }
> > 4 } Intermediates from smoutpoutn (f called 4 times)
> > 8 }
> > 16 }
> > 16 NB. Result returned (ran to completion)
> > f^:(10>])^:8 ] 1
> > 2 }
> > 4 } Intermediates from smoutput (f called 4 times)
> > 8 }
> > 16 }
> > 16 NB. Result returned (aborted, so it stopped short
> > and did not proceed further)
> >
> > HTH, Rob
> >
> >
> > > On 26 May 2020, at 6:40 pm, Anton Wallgren <[email protected]> wrote:
> > >
> > > 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
> >
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
> ----------------------------------------------------------------------
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