On 30 set, 09:35, namekuseijin <namekusei...@gmail.com> wrote: > On 29 set, 11:04, w_a_x_man <w_a_x_...@yahoo.com> wrote: > > > > > On Sep 26, 9:24 am, p...@informatimago.com (Pascal J. Bourguignon) > > wrote: > > > > Xah Lee <xah...@gmail.com> writes: > > > > here's a interesting toy list processing problem. > > > > > I have a list of lists, where each sublist is labelled by > > > > a number. I need to collect together the contents of all sublists > > > > sharing > > > > the same label. So if I have the list > > > > > ((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q > > > > r) (5 s t)) > > > > > where the first element of each sublist is the label, I need to > > > > produce: > > > > > output: > > > > ((a b) (c d i j) (e f k l o p) (g h) (m n q r) (s t)) > > > > > a Mathematica solution is here: > > > >http://xahlee.org/UnixResource_dir/writ/notations_mma.html > > > > > R5RS Scheme lisp solution: > > > >http://xahlee.org/UnixResource_dir/writ/Sourav_Mukherjee_sourav.work_... > > > > by Sourav Mukherjee > > > > > also, a Common Lisp solution can be found here: > > > >http://groups.google.com/group/comp.lang.lisp/browse_frm/thread/5d1de... > > > > It's too complex. Just write: > > > > (let ((list '((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) > > > (2 o p) (4 q r) (5 s t)))) > > > > (mapcar (lambda (class) (reduce (function append) class :key (function > > > rest))) > > > (com.informatimago.common-lisp.list:equivalence-classes list > > > :key (function first))) > > > > ) > > > > --> ((S T) (Q R M N) (G H) (O P K L E F) (I J C D) (A B)) > > > > -- > > > __Pascal Bourguignon__ http://www.informatimago.com/ > > > Ruby: > > > [[0, 'a', 'b'], [1, 'c', 'd'], [2, 'e', 'f'], [3, 'g', 'h'], [1, > > 'i', 'j'], [2, 'k', 'l'], [4, 'm', 'n'], [2, 'o', 'p'], [4, 'q', 'r'], > > [5, 's', 't']]. > > group_by{|x| x.first}.values.map{|x| x.map{|y| y[1..-1]}.flatten} > > > ==>[["s", "t"], ["a", "b"], ["c", "d", "i", "j"], > > ["e", "f", "k", "l", "o", "p"], > > ["g", "h"], ["m", "n", "q", "r"]] > > cool, it comes with order all fucked up. This is something I was > criticized for before, though not all that important to most > functional processing. Not the case here, though. > > here's a scheme version that is hopefully better than the given one:
(define (dig in) (if (null? in) '() (let* ((n (first-of-first in)) (all-n (filter in (lambda (x) (eq? n (first x))))) (all-but-n (filter in (lambda (x) (not (eq? n (first x))))))) (pair (fold all-n (lambda (i o) (pair (second i) (pair (third i) o)))) (dig all-but-n))))) ; given these aliases to lisp n00bs (define pair cons) (define first car) (define rest cdr) (define first-of-first caar) (define second cadr) (define third caddr) ; and these well-known functions (non-tail-recursive for benefit of n00bs) (define (fold ls f) ; AKA reduce (if (null? ls) '() (f (first ls) (fold (rest ls) f)))) (define (filter ls f) (fold ls (lambda (i o) (if (f i) (pair i o) o)))) ; testing (let ((in '((0 a b) (1 c d) (2 e f) (3 g h) (1 i j) (2 k l) (4 m n) (2 o p) (4 q r) (5 s t)))) (display (dig in)) (newline)) ;frakkin text editor... -- http://mail.python.org/mailman/listinfo/python-list
