hash-update is defined in Racket and, besides the error checking, is basically the composition of those two functions. I expect it was written as something to abstract over a common pattern, not speed things up.
Is this a bottleneck in some real program? Perhaps you'd share that (or some inner loop of it)? I wonder if there is a better way to speed it up than this. Robby On Thu, Feb 14, 2013 at 1:09 PM, J. Ian Johnson <i...@ccs.neu.edu> wrote: > If I am right, then it would make sense to use hash-update when the hash > is big enough that a log-time traversal takes longer than a general > procedure call's set-up and tear-down. > -Ian > ----- Original Message ----- > From: James Bergstra <james.bergs...@gmail.com> > To: J. Ian Johnson <i...@ccs.neu.edu> > Cc: users@racket-lang.org > Sent: Thu, 14 Feb 2013 13:47:51 -0500 (EST) > Subject: Re: [racket] Question about hash table efficiency > > Thanks, I suppose I just had my hopes up. I thought the more compact > form might involve fewer expression evaluations and require just one > hash lookup instead of two, and therefore might run something like > twice as fast, rather than slightly slower. > > On Thu, Feb 14, 2013 at 1:36 PM, J. Ian Johnson <i...@ccs.neu.edu> wrote: > > My guess would be the higher-orderness on hash-update causes the (minor) > slowdown. > > -Ian > > ----- Original Message ----- > > From: James Bergstra <james.bergs...@gmail.com> > > To: users@racket-lang.org > > Sent: Thu, 14 Feb 2013 13:16:47 -0500 (EST) > > Subject: [racket] Question about hash table efficiency > > > > Hi list, just discovered racket and having fun learning about scheme > > again. Haven't used it since undergrad. Thanks! > > > > I was wondering about the efficiency of hash-update vs. hash-set and > > hash-ref. I thought the former would be faster, otherwise why have it? > > A little benchmark script reveals the same surprising result as my > > actual application though: > > > > """ > > #lang racket > > > > ;; warm-up > > (time (void > > (for/fold ([table (make-immutable-hasheq '())]) > > ([ii (in-range 100000)]) > > (hash-update table (modulo ii 100) add1 ii)))) > > > > ;; update > > (newline) > > (time (void > > (for/fold ([table (make-immutable-hasheq '())]) > > ([ii (in-range 100000)]) > > (hash-update table (modulo ii 100) add1 ii)))) > > > > ;; set/ref > > (newline) > > (time (void > > (for/fold ([table (make-immutable-hasheq '())]) > > ([ii (in-range 100000)]) > > (hash-set table (modulo ii 100) (add1 (hash-ref table (modulo ii 100) > ii)))))) > > > > """ > > > > This prints out: > > > > cpu time: 112 real time: 114 gc time: 32 > > > > cpu time: 80 real time: 82 gc time: 0 > > > > cpu time: 76 real time: 75 gc time: 4 > > > > > > My original application used mutable hash tables and the same effect > > was observed (if not more dramatically). Any thoughts on why the > > update form is slower? I'm running this in Racket v5.1.1. > > > > - James > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users >
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