[racket] Performance help

Would it help to use an eq? hash and turn all of the strings into
symbols (hopefully up front)? That might make the hashing part faster
in the best-known function. (Also, you can use two accumulators in the
for*/fold instead of one to avoid creating 'cons' cells but that seems
unlikely to matter much.)

Robby

On Fri, Jan 2, 2015 at 1:44 PM, Greg Hendershott
<greghendershott at gmail.com> wrote:
> Although it can't hurt, I don't think `train` comes close to
> dominating the time?
>
> Through the sophisticated profiling technique of commenting-out `or`
> branches in `correct`, I got the sense that the third one is the
> issue:
>
>
> (define (correct m s)
>   (let ([best-known (λ (xs) (best-known m xs))])
>     (or (best-known (list s))
>         (best-known (edits1 s))
>         (best-known (append-map edits1 (edits1 s))) <-- if reached, very slow
>         s)))
> real    0m16.527s
> user    0m14.554s
> sys     0m1.859s
>
>
> (define (correct m s)
>   (let ([best-known (λ (xs) (best-known m xs))])
>     (or (best-known (list s))
>         (best-known (edits1 s))
>         (best-known (edits2 m s)) ;; what I posted yesterday
>         s)))
> real    0m9.807s
> user    0m9.463s
> sys     0m0.266s
>
>
> (define (correct m s)
>   (let ([best-known (λ (xs) (best-known m xs))])
>     (or (best-known (list s))
>         (best-known (edits1 s))
>         ;; (best-known (edits2 m s)) ;; skip it entirely
>         s)))
> real    0m2.074s
> user    0m1.708s
> sys     0m0.184s
>
>
> p.s. `best-known` = combining `best` and `known` into a single pass for/fold:
>
> ;; Given a hash map and a list of words, returns
> ;; one of the words with the highest frequency.
> ;; Given an empty list returns #f
> (define (best-known ht xs)
>   (car (for*/fold ([best (cons #f 0)])
>                   ([x (in-list xs)]
>                    [v (in-value (hash-ref ht x #f))] ;; should default be 1?
>                    #:when v)
>          (if (> v (cdr best)) (cons x v) best))))
>
> ... which I thought might be faster but wasn't significant.
>
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