performance is about the same when each is used instead, and not so different
from "0
timespacex ']`+:@.(2&|) each i.1000'
0.000423999 509056
timespacex '+:^:(2&|) each i.1000'
0.000448319 300416
timespacex '+:^:(2&|)"0 i.1000'
0.000360319 19968
timespacex '+:^:(2&|) every i.1000'
0.000480319 20224
timespacex ']`+:@.(2&|) every i.1000'
0.000423359 20736
there is a large space difference with each but not with every.
----- Original Message -----
From: Dan Bron <[email protected]>
To: J Programming <[email protected]>
Sent: Monday, January 4, 2016 12:13 PM
Subject: Re: [Jprogramming] a performance quirk
Performance analysis requires a kind of triage. The first thing that sticks out
about both expressions is that “0 . We need to excise that first: J is a
language that expects and rewards thinking big.
(;:'Verb TimeX SpaceX') , V ,. '0.2' 8!:0 (%"1 <./) Q=:100 timespacex&> ' D'
,L:0~ V=: '+:^:(2&|)"0';']`+:@.(2&|)"0';'(* 1+2&|)'
+-------------+-----+------+
|Verb |TimeX|SpaceX|
+-------------+-----+------+
|+:^:(2&|)"0 |34.71| 1.00 |
+-------------+-----+------+
|]`+:@.(2&|)"0| 3.70| 5.75 |
+-------------+-----+------+
|(* 1+2&|) | 1.00| 2.00 |
+-------------+-----+———+
Having said that, the ~35x slowdown (vs ~4x for @.) is more than a little
surprising. The very specific 2x space improvement over the array solution is
likely telling us something about what’s going on, but I haven’t quite thought
through what it is yet.
-Dan
> On Dec 28, 2015, at 1:48 PM, 'Pascal Jasmin' via Programming
> <[email protected]> wrote:
>
> timespacex '+:^:(2&|)"0 i.100000'
> 0.0292787 2.10074e6
> timespacex ']`+:@.(2&|)"0 i.100000'
> 0.00561727 7.08134e6
>
> above code doubles odd numbers, and returns even numbers unchanged.
>
>
> I've previously noticed that ^: seemd faster than ]`u@. ... but I guess not?
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