Rather simple list/set operation [?]

From: Drew Krause
Subject: rather simple list/set operation
Date: Tue, 3 Jan 2012 19:01:19 -0600


Drew Krause wrote:

Maybe someone can help me with this?
 
I start with a list, e.g.
 
((0) (1 3) (1 2) (4 6) (5 7) (7 8))
 
 
and want all members of intersecting lists to appear in the same sublist:
 
=> ((0) (1 2 3) (4 6) (5 7 8))

Gauche Scheme:

(use srfi-1)  ; "lset-" functions
(use srfi-42) ; do-ec

(define (coalesce lists)
  (define accum '())
  (do-ec (:list x lists)
    (receive
      (miss hit)
      (partition (lambda (y) (null? (lset-intersection equal? x y)))
                 accum)
        (set! accum
          (cons (apply lset-union equal? x hit) miss))))
  accum)


(coalesce '((2 4)    (8 9) (4 5 8)))
  ===>
((2 9 4 5 8))

(coalesce '((2 4) (3 9) (5 6) (2 3)))
 ===>
((4 9 2 3) (5 6))

(coalesce '((0) (1 3) (1 2) (4 6) (5 7) (7 8)))
 ===>
((5 7 8) (4 6) (3 1 2) (0))

(coalesce '((2 4) (3 9) (5 6) (2 3) (55 66) (0) (66 6)))
 ===>
((5 55 66 6) (0) (4 9 2 3))