From Newsgroup: comp.lang.lisp

B. Pym wrote:

B. Pym wrote:

Kenny Tilton wrote:

(defun p2b (pairs &key ((:test test) #'eql))
"((A 1) (A 2) (B 2) (C 2) (C 3)) ==> ((A 1 2) (B 2) (C 2 3))"
(loop with bunch = nil
for (one two) in pairs
do (push two (cdr (or (assoc one bunch :test test)
(car (push (list one) bunch)))))
finally (return bunch)))

Testing:

(p2b '((A 1) (A 2) (B 2) (C 2) (C 3) (A 88)))
===>
((C 3 2) (B 2) (A 88 2 1))

Gauche Scheme

Let's use a collector that collects into an association-list.

(let ((a (malistbag)))
(for-each
(lambda(xs) (apply a `(,@xs ,cons ())))
'((A 1) (A 2) (B 2) (C 2) (C 3) (A 88)))
(a))

Given:

Another way.

(define (p2b pairs :optional (test equal?))
(define alist (map list (delete-duplicates (map car pairs))))
(define (proc k v) (push! (cdr (assoc k alist test)) v))
(dolist (e pairs) (apply proc e))
alist)

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