My guess would be that it has something to do with cache coherence. Indexing is random access, sorting is more sequential in nature.
But that's just a guess, because I did not cheat and look at the source or anything (at least... not today). Thanks, -- Raul On Wed, Mar 5, 2014 at 2:45 PM, Roger Hui <[email protected]> wrote: > That's my alternative faster expression as well. But the more interesting > question is, why is it faster? Since we do the grade in both cases, the > comparison is between /:~x and g{x (or x{~g) with g pre-computed. The > answer does not depend knowledge specific to J. > > > > > > On Wed, Mar 5, 2014 at 11:38 AM, Joe Bogner <[email protected]> wrote: > > > Sorting and grading separately seems faster > > > > timer=: 6!:2 > > x=:(1e7 $ 26?26) { 'abcdefghijklmnopqrstuvwxyz' > > NB. incumbent > > timer 's=: x{~g=: /:x' > > 0.0914002 > > > > NB. alternate > > timer 'S=: /:~x[G=: /:x' > > 0.0668677 > > > > s-:S > > 1 > > G-:g > > 1 > > > > > > I am speculating that sorting does it in place? which is faster than > > the selection from the grade > > > > > > > > On Wed, Mar 5, 2014 at 2:02 PM, Raul Miller <[email protected]> > wrote: > > > Hmm... > > > > > > G=:a.i.S=:/:~x > > > is faster. > > > > > > But while s-:S, g and G are different. > > > > > > So I'm drawing a blank here, on how to make the grade. > > > > > > Thanks, > > > > > > -- > > > Raul > > > > > > > > > > > > On Wed, Mar 5, 2014 at 1:52 PM, Roger Hui <[email protected]> > > wrote: > > > > > >> Suppose x is a long vector of characters and you need both its sort > and > > its > > >> grade. Can you do it faster than s=: x{~g=: /:x ? > > >> > > >> Posed this way, the answer is of course yes. But how, and why is it > > >> faster? > > >> ---------------------------------------------------------------------- > > >> 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
