| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

UNUMS (Universal Number Format); MOOCs (Massive Open Online Courses); Interesting Looking Game; Euler's Theorem for Polynomials; Weeks 3-6; Reddit Comment; Differential Cryptanalysis For Dummies; Japanese Graphic Design; Books To Be Re-Read; And Today I Learned Bugs Need Clear Examples; Factoring a 67 bit prime in your head; Islamic Geometric Art; Useful Julia Backtraces from Tasks; Nothing, however, is lost with less discomfort than that which, when lost, cannot be missed; Article on Didion; Cost of Living by City; British Slavery; Derrida on Metaphor; African SciFi; Traits in Julia; Alternative Japanese Lit; Pulic Key as Address (Snow); Why Information Grows; The Blindness Of The Chilean Elite; Some Victoriagate Links; This Is Why I Left StackOverflow; New TLS Implementation; Maths for Physicists; How I Am 8; 1000 Word Philosophy; Cyberpunk Reading List; Detailed Discussion of Message Dispatch in ParserCombinator Library for Julia; FizzBuzz in Julia w Dependent Types; kokko - Design Shop in Osaka; Summary of Greece, Currently; LLVM and GPUs; See Also; Schoolgirl Groyps (Maths); Japanese Lit; Another Example - Modular Arithmetic; Music from United; Python 2 and 3 compatible alternative.; Read Agatha Christie for the Plot; A Constructive Look at TempleOS; Music Thread w Many Recommendations; Fixed Version; A Useful Julia Macro To Define Equality And Hash; k3b cdrom access, OpenSuse 13.1; Week 2; From outside, the UK looks less than stellar; Huge Fonts in VirtualBox; Keen - Complex Emergencies; The Fallen of World War II; Some Spanish Fiction; Calling C From Fortran 95; Bjork DJ Set; Z3 Example With Python; Week 1; Useful Guide To Starting With IJulia; UK Election + Media; Review: Reinventing Organizations; Inline Assembly With Julia / LLVM; Against the definition of types; Dumb Crypto Paper; The Search For Quasi-Periodicity...; Is There An Alternative To Processing?; CARDIAC (CARDboard Illustrative Aid to Computation); The Bolivian Case Against Chile At The Hague; Clear, Cogent Economic Arguments For Immigration; A Program To Say If I Am Working; Decent Cards For Ill People; New Photo; Luksic And Barrick Gold; President Bachelet's Speech; Baltimore Primer; libxml2 Parsing Stream; configure.ac Recipe For Library Path; The Davalos Affair For Idiots; Not The Onion: Google Fireside Chat w Kissinger; Bicycle Wheels, Inertia, and Energy; Another Tax Fraud; Google's Borg; A Verion That Redirects To Local HTTP Server; Spanish Accents For Idiots; Aluminium Cans; Advice on Spray Painting; Female View of Online Chat From a Male; UX Reading List; S4 Subgroups - Geometric Interpretation; Fucking Email; The SQM Affair For Idiots; Using Kolmogorov Complexity; Oblique Strategies in bash; Curses Tools; Markov Chain Monte Carlo Without all the Bullshit; Email Para Matias Godoy Mercado; The Penta Affair For Idiots; Example Code To Create numpy Array in C; Good Article on Bias in Graphic Design (NYTimes); Do You Backup github?; Data Mining Books

© 2006-2015 Andrew Cooke (site) / post authors (content).

Permute Fucntion (Scheme)

From: "andrew cooke" <andrew@...>

Date: Tue, 14 Aug 2007 22:53:01 -0400 (CLT)

":";exec snow -- "$0" "$@"

(package* permute/v1.0.0
  (provide: (define (permute lst))))

; generates a list of all permutations
; assumes all values in original list are unique (under equal?)
(define (permute lst)
  (case (length lst)
    ((0) '())
    ((1) (list lst))
    (else (flat-map (lambda (head)
                      (map (lambda (perm) (cons head perm))
                           (permute (except head lst))))
                    lst))))

(define (flat-map f lst) (flat-map-acc f lst '()))
(define (flat-map-acc f lst acc)
  (if (null? lst)
      acc
      (flat-map-acc f (cdr lst) (append acc (f (car lst))))))

; this does not attempt to keep any kind of ordering
(define (except x lst) (except-acc x lst '()))
(define (except-acc x lst acc)
  (if (null? lst)
      acc
      (let ((head (car lst))
            (tail (cdr lst)))
        (if (equal? x head)
            (append acc tail)
            (except-acc x tail (cons head acc))))))


(test*
 (define (dup x) (list x x))
 (expect* (equal? '() (flat-map dup '())))
 (expect* (equal? '(1 1) (flat-map dup '(1))))
 (expect* (equal? '(1 1 2 2) (flat-map dup '(1 2)))))

(test*
 (expect* (equal? '() (except 0 '())))
 (expect* (equal? '() (except 1 '(1))))
 (expect* (equal? '(2) (except 1 '(1 2))))
 (expect* (equal? '(3 2 1) (except 0 '(1 2 3))))
 (expect* (equal? '(2 3) (except 1 '(1 2 3))))
 (expect* (equal? '(1 3) (except 2 '(1 2 3))))
 (expect* (equal? '(2 1) (except 3 '(1 2 3)))))

(test*
 (expect* (equal? '() (permute '())))
 (expect* (equal? '((1)) (permute '(1))))
 (expect* (equal? '((1 2)(2 1)) (permute '(1 2))))
 (expect* (equal? '((1 2 3)(1 3 2)(2 1 3)(2 3 1)(3 2 1)(3 1 2))
                  (permute '(1 2 3)))))

Improved Permutation Function (Start of List Library)

From: "andrew cooke" <andrew@...>

Date: Wed, 15 Aug 2007 12:07:38 -0400 (CLT)

":";exec snow -- "$0" "$@"

; library of list-related functions

(package* ac-lists/v1.0.0
  (provide:
      ; abstract the typical patter used to recurse over lists
      (define-syntax acl-list-process
        (syntax-rules (null?)
          ((_ ((null? list) null-body)
              ((head tail) body))
           (if (null? list)
               null-body
               (let ((head (car list))
                     (tail (cdr list)))
                 body)))))
    (define (acl-filter pred lst))
    (define (acl-filter-acc pred lst acc))
    (define (acl-except x lst))
    (define (acl-flat-map fun lst))
    (define (acl-flat-map-acc fun lst acc))
    (define (acl-permute lst))
    ))

; remove all values that match predicate from a list
(define (acl-filter pred lst) (reverse (acl-filter-acc pred lst '())))
(define (acl-filter-acc pred lst acc)
  (acl-list-process
   ((null? lst) acc)
   ((head tail) (if (pred head)
                    (acl-filter-acc pred tail acc)
                    (acl-filter-acc pred tail (cons head acc))))))

(test*
 (define (one? x) (= 1 x))
 (expect* (equal? '() (acl-filter one? '())))
 (expect* (equal? '() (acl-filter one? '(1))))
 (expect* (equal? '(2) (acl-filter one? '(2))))
 (expect* (equal? '(2 3) (acl-filter one? '(2 1 3)))))

; exclude instances of a particular value
(define (acl-except x lst) (acl-filter (lambda (y) (equal? x y)) lst))

(test*
 (expect* (equal? '() (acl-except 0 '())))
 (expect* (equal? '() (acl-except 1 '(1))))
 (expect* (equal? '(2) (acl-except 1 '(1 2))))
 (expect* (equal? '(1 2 3) (acl-except 0 '(1 2 3)))))

; map with append instead of cons
(define (acl-flat-map fun lst) (reverse (acl-flat-map-acc fun lst '())))
(define (acl-flat-map-acc fun lst acc)
  (acl-list-process
   ((null? lst) acc)
   ((head tail) (acl-flat-map-acc fun tail (append (fun head) acc)))))

(test*
 (define (dup x) (list x x))
 (expect* (equal? '() (acl-flat-map dup '())))
 (expect* (equal? '(1 1) (acl-flat-map dup '(1))))
 (expect* (equal? '(1 1 2 2) (acl-flat-map dup '(1 2)))))

; a list of all permutations
; assumes all values in original list are unique (under equal?)
(define (acl-permute lst)
  (define (perm-rest x)
    (define (cons-x rest) (cons x rest))
    (let ((rest (acl-except x lst)))
      (map cons-x (acl-permute rest))))
  (acl-list-process
   ((null? lst) '())
   ((head tail) (if (null? tail)
                    (list lst)
                    (acl-flat-map perm-rest lst)))))

(test*
 (expect* (equal? '() (acl-permute '())))
 (expect* (equal? '((1)) (acl-permute '(1))))
 (expect* (equal? '((1 2)(2 1)) (acl-permute '(1 2))))
 (expect* (equal? '((1 3 2)(1 2 3)(2 3 1)(2 1 3)(3 2 1)(3 1 2))
                  (acl-permute '(1 2 3)))))

Comment on this post