[racket] performance of iteration through a vector

All,

Thanks for the pointer to (in-vector). It indeed works faster than
the explicit (vector-ref) or even (unsafe-vector-ref).

And yes, I should get around to Typed Racket someday.

Regards,

Dmitry




On Sun, Aug 31, 2014 at 9:19 AM, Robby Findler <robby at eecs.northwestern.edu>
wrote:

> Or, use typed racket.
>
> Robby
>
> On Sat, Aug 30, 2014 at 8:18 PM, Matthew Butterick <mb at mbtype.com> wrote:
> > Usually you'll get the best performance from `for` loops by using the
> in-*
> > iterators.
> > In this case, you can use `in-vector` [1], which on my machine is faster:
> >
> > (let ((t (current-inexact-milliseconds))
> >       (sum 0))
> >   (for ((j (in-range 1000000)))
> >     (for ((v (in-vector vec)))
> >       (set! sum (+ sum v))))
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> > I assume this is a synthetic example, but you can also improve
> performance
> > by using appropriate versions of `for`. This is faster than the last one:
> >
> > (let ((t (current-inexact-milliseconds)))
> >   (for*/fold ([sum 0])([j (in-range 1000000)][v (in-vector vec)])
> >     (+ sum v))
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> > And this is faster still:
> >
> > (let ((t (current-inexact-milliseconds)))
> >   (for*/sum ([j (in-range 1000000)][v (in-vector vec)])
> >     v)
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> >
> > [1]
> >
> http://docs.racket-lang.org/reference/sequences.html?q=in-vector#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-vector%29%29
> >
> >
> > On Aug 30, 2014, at 3:54 PM, Dmitry Pavlov <dpavlov at ipa.nw.ru> wrote:
> >
> > Hello,
> >
> > Consider the following program:
> >
> > (define n 100)
> > (define vec (for/vector ((i (in-range n))) i))
> >
> > (let ((t (current-inexact-milliseconds))
> >       (sum 0))
> >   (for ((j (in-range 1000000)))
> >     (for ((i (in-range n)))
> >       (set! sum (+ sum (vector-ref vec i)))))
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> > (let ((t (current-inexact-milliseconds))
> >       (sum 0))
> >   (for ((j (in-range 1000000)))
> >     (for ((v vec))
> >       (set! sum (+ sum v))))
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> >
> > On my system (64-bit linux, Racket 6.1.0.2), it gives the following
> result:
> >
> > 1.016682861328125
> > 6.3261611328125
> >
> >
> > So we can make a conclusion that (for ((v vec)) ...) is
> > 6x slower than (for ((i (in-range n))) ... (vector-ref vec i) ...)
> > Is it normal? Would you advise to use the explicit (vector-ref)
> > when performance matters?
> >
> > Best regards
> >
> > Dmitry
> >
> > ____________________
> >  Racket Users list:
> >  http://lists.racket-lang.org/users
> >
> >
> >
> >
> > On Aug 30, 2014, at 3:54 PM, Dmitry Pavlov <dpavlov at ipa.nw.ru> wrote:
> >
> > Hello,
> >
> > Consider the following program:
> >
> > (define n 100)
> > (define vec (for/vector ((i (in-range n))) i))
> >
> > (let ((t (current-inexact-milliseconds))
> >       (sum 0))
> >   (for ((j (in-range 1000000)))
> >     (for ((i (in-range n)))
> >       (set! sum (+ sum (vector-ref vec i)))))
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> > (let ((t (current-inexact-milliseconds))
> >       (sum 0))
> >   (for ((j (in-range 1000000)))
> >     (for ((v vec))
> >       (set! sum (+ sum v))))
> >   (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
> >
> >
> > On my system (64-bit linux, Racket 6.1.0.2), it gives the following
> result:
> >
> > 1.016682861328125
> > 6.3261611328125
> >
> >
> > So we can make a conclusion that (for ((v vec)) ...) is
> > 6x slower than (for ((i (in-range n))) ... (vector-ref vec i) ...)
> > Is it normal? Would you advise to use the explicit (vector-ref)
> > when performance matters?
> >
> > Best regards
> >
> > Dmitry
> >
> > ____________________
> >  Racket Users list:
> >  http://lists.racket-lang.org/users
> >
> >
> >
> > ____________________
> >   Racket Users list:
> >   http://lists.racket-lang.org/users
> >
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users
>
>
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