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
