Oh yeah, duh.
On Thu, Oct 14, 2010 at 12:48 PM, Matthias Felleisen <matth...@ccs.neu.edu> wrote: > > Because (require racket) provides everything you'd ever want. > > > On Oct 14, 2010, at 12:39 PM, Nadeem Abdul Hamid wrote: > >>> Thanks for setting my head straight! >> >> >> Oh, I wasn't meaning to do that! :) >> >> Incidentally, why does your solution run even when the language level >> is set to "Intermediate Student"? In fact, even mine runs in ISL while >> I use lambda. I'm running DrRacket, version 5.0.1.7--2010-10-06. >> >> --- nadeem >> >> >> On Thu, Oct 14, 2010 at 12:29 PM, Matthias Felleisen >> <matth...@ccs.neu.edu> wrote: >>> >>> I ran this stress test for your 5 line solution and mine: >>> >>>> (define *the-list* (build-list 10000000 (lambda (i) (random (+ i 1))))) >>>> (time (______ *the-list*)) >>> >>> For small benchmarks, your solution may take twice as long as my 8 line ASL >>> solution, >>> but for something of the above size -- there can't be that many lakes in MN >>> -- it takes >>> almost the same time. >>> >>> In short, don't be afraid of 10 iterations over long lists, and don't >>> bother with >>> hash tables and fancy algorithmics until you know you need it -- by >>> measuring. >>> >>> I used to believe this but have temporarily forgotten this lesson due to >>> external influences. >>> >>> -- Matthias >>> >>> >>> >>> >>> On Oct 14, 2010, at 12:09 PM, Nadeem Abdul Hamid wrote: >>> >>>> Here's a solution in ISL: >>>> >>>> ;; benson : [listof positive-number] -> [listof (list number number)] >>>> (define (benson a-lon) >>>> (let ([digs (map (compose >>>> string->number first explode number->string >>>> exact->inexact) a-lon)]) >>>> (build-list 10 >>>> (λ(i) (list i >>>> (/ (length (filter (λ(d) (= i d)) digs)) >>>> (length digs))))))) >>>> >>>> >>>> ;; TESTS (matthias' and jay's, modified) >>>> >>>> (require racket) ; (only-in ... for/list) >>>> >>>> (check-expect (filter (lambda (p) (not (zero? (second p)))) >>>> (benson '(123 124 125 126 23 24 31))) >>>> (list (list 1 4/7) (list 2 2/7) (list 3 1/7))) >>>> >>>> (check-expect >>>> (benson (list 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.10 >>>> 11 12 13 14 15 16 17 18 19 >>>> 21 22 23 24 25 26 27 28 >>>> 31 32 33 34 35 36 37 >>>> 41 42 43 44 45 46 >>>> 51 52 54 54 55 >>>> 61 62 63 64 >>>> 71 72 73 >>>> 81 82 >>>> 91)) >>>> (for/list ([i (in-range 10)]) >>>> (list i >>>> (/ (- 10 i) >>>> (+ 10 9 8 7 6 5 4 3 2 1)))) >>>> ) >>>> >>>> >>>> >>>> >>>> On Thu, Oct 14, 2010 at 11:30 AM, Matthias Felleisen >>>> <matth...@ccs.neu.edu> wrote: >>>>> >>>>> >>>>> I love this solution but let me supply a solution in ASL, the teaching >>>>> language: >>>>> >>>>> >>>>> ;; ASL >>>>> (require racket) ; (only-in ... hash->list) >>>>> ;; I could have used the key for sort to get around the second lambda >>>>> >>>>> ;; [Listof String] -> [Listof (cons Digit Nat)] >>>>> ;; compute a frequency count of the leading digit in the number of lon >>>>> ;; assume: the digits are positive >>>>> (define (collect lon) >>>>> (local ((define loch (map (compose string->list number->string) lon)) >>>>> (define (upd c H) (hash-set H c (+ (hash-ref H c 0) 1))) >>>>> (define hash (foldl (lambda (x H) (upd (first x) H)) #hash() >>>>> loch)) >>>>> (define loh# (hash->list hash)) >>>>> (define srtd (sort loh# (lambda (l r) (> (cdr l) (cdr r)))))) >>>>> (map (lambda (x) (cons (string->number (string (car x))) (cdr x))) >>>>> srtd))) >>>>> >>>>> (check-expect (collect '(123 124 125 126 23 24 31)) >>>>> (list (cons 1 4) (cons 2 2) (cons 3 1))) >>>>> >>>>> >>>>> If actual I/O is required, I'd use batch-io to read CSV files and >>>>> display the list above in a batch action. >>>>> _________________________________________________ >>>>> For list-related administrative tasks: >>>>> http://lists.racket-lang.org/listinfo/users >>>>> >>>> >>>> > > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
