Virtual blocks started in 8.07 and were finished in 9.01; not so many years.
Look at
https://code.jsoftware.com/wiki/Vocabulary/SpecialCombinations#Virtual_Nouns
and
https://code.jsoftware.com/wiki/Vocabulary/SpecialCombinations#Execution_In_Place_.28EIP.29
for some rules that will save time and space, and at the rest of
https://code.jsoftware.com/wiki/Vocabulary/SpecialCombinations
for the special forms the interpreter knows about.
Henry Rich
On 5/16/2020 7:07 PM, 'Michael Day' via Programming wrote:
So have we all (mostly) been wrong over all the years in reporting,
and comparing,
ts, and the like, to assess which is the "best" version of some
verb? We had all,
mostly?, learnt to assign the input outside the ts argument, but
that's only the
foothills, apparently.
I don't think it's just me this evening. Seems worth a chapter or two
of J wiki or
NuBenchMark or the like...
Thanks for the instructive ticking-off,
Cheers,
Mike
On 16/05/2020 23:43, bill lam wrote:
Shouldn't assignment like
b=. , a
c=. 1{a
just increase reference count of the mother instead of deep copy?
On Sun, May 17, 2020, 6:27 AM Henry Rich <[email protected]> wrote:
I wouldn't say so. Reshape takes virtually no time/space, but
boxing or
assigning the reshaped result does. If you do something like
+/ @: (,/) y
the result of ,/ is never realized and it would be wrong to charge it
with time/space not used.
Similarly
(}. - }:) y
the }. and }: create virtual results that are never realized.
You need to expand your mental model beyond time/space for a verb, to
include time/space for realization when that becomes necessary.
Henry Rich
On 5/16/2020 1:22 PM, 'Mike Day' via Programming wrote:
Oh... so one needs to, say, assign the result to see the real t/s?
Thanks,
Mike
Sent from my iPad
On 16 May 2020, at 17:05, Henry Rich <[email protected]> wrote:
The time/space numbers are telling you that (x $ y) produces a
virtual
result when it can, while (_2 ]\ y) doesn't (yet). If you use the
result
immediately, the space saving is real. If you box the result or
save it in
a name, the value will be realized and the space saving will vanish.
Henry Rich
On 5/16/2020 11:14 AM, 'Michael Day' via Programming wrote:
Much neater than what I was about to offer, unless Raoul needs to
specify the fill,
in which case, this alternative rather minimal amendment is worth
consideration:
($!._ ~2,~>.@-:@#) i.7
0 1
2 3
4 5
6 _
cf
_2]\ i.7
0 1
2 3
4 5
6 0
Also, the time and space performance _might_ be important for large
inputs:
ts' $ _2]\ list ' [list =: i.100000
0.000618 1.04986e6
ts'($!._ ~2,~>.@-:@#) list'
2.7e_6 2304
Cheers,
Mike
On 16/05/2020 15:57, 'Rob Hodgkinson' via Programming wrote:
You could try Infix … here with NuVoc link…
https://code.jsoftware.com/wiki/Vocabulary/bslash#dyadic
x u\ y where x is eg _2 means apply very b to successive
pairs
(_ for non-overlapping).
_2 ]\ 1 2 3 4 5 6
1 2
3 4
5 6
_2 ]\ 1 2 3 4 5 6 7
1 2
3 4
5 6
7 0
_2 <\ 1 2 3 4 5 6
┌───┬───┬───┐
│1 2│3 4│5 6│
└───┴───┴───┘
HTH…/Rob
On 17 May 2020, at 12:42 am, Raoul Schorer
<[email protected]>
wrote:
Hello,
I am convinced that this must be trivial, but I wasn't able to
find
in the documentation how to reshape a list to a table without manually
extracting the length.
in summary, is there a more direct way of doing:
lst =. i. 6
((2,~2%~#) $ ]) lst
for a list of arbitrary length?
Thanks!
Raoul
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