x($,)y does make a copy of the values of y, as the following session illustrates:
7!:0 '' 2107136 x=: 3 1 4 1 5 9 265358 $ 0.2 7!:0 '' 2149590784 t=: x 7!:0 '' 2149590912 NB. i.e. did not make a copy to make t x1=: (($-.1:) ($,) ]) x 7!:0 '' 4297074688 NB. i.e. made a copy to make x1 Or this: timer=: 6!:2 timer 'x1=: (($-.1:) ($,) ]) x' 0.574603 If it did not make a copy it wouldn't have taken so much time to make x1. On Tue, Mar 4, 2014 at 3:10 PM, Dan Bron <[email protected]> wrote: > What Roger so humbly neglected to brag about is the hook ($,) is supported > by special code. > > In effect, the verb he provided will be instantaneous: ($,) simply updates > the tiny piece of memory holding the array's shape with the new shape. > > The value part of the array won't be touched, or even looked at. > > -Dan > > > > > On Mar 4, 2014, at 4:59 PM, Brian Schott <[email protected]> wrote: > > > > That's funny. I almost said what you did. Thanks. > > > > > >> On Tue, Mar 4, 2014 at 4:44 PM, Roger Hui <[email protected]> > wrote: > >> > >> f=: ($ -. 1:) ($,) ] > >> $ f 3 1 4 1 5 9 $ 'abc' > >> 3 4 5 9 > >> > >> > >> > >> On Tue, Mar 4, 2014 at 1:38 PM, Brian Schott <[email protected]> > >> wrote: > >> > >>> Is there a general verb that can reshape any noun with 1s in its shape > so > >>> that the axes with 1s disappear? I know that most often changing > >>> calculations slightly can eliminate the 1s before they arise, but not > >>> always. > >>> > >>> For example if $a == 4 1 4 3, is there a verb that will > >>> make generalize the result like how ,"_2]1|: does in this case? > >>> $,"_2]1|:a == 4 4 3 > >>> > >>> -- > >>> (B=) > >>> ---------------------------------------------------------------------- > >>> For information about J forums see http://www.jsoftware.com/forums.htm > >> ---------------------------------------------------------------------- > >> For information about J forums see http://www.jsoftware.com/forums.htm > > > > > > > > -- > > (B=) <-----my sig > > Brian Schott > > ---------------------------------------------------------------------- > > 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
