Re: Any way to collect all the values of a hash table more concisely ?

B. Pym wrote:

So this new version works as intended:

 

(defun cluster-by (fn list &aux (clusters (make-hash-table)) (result nil))
    (mapcar #'(lambda (x) (push x (gethash (funcall fn x) clusters))) list)
    (maphash  #'(lambda (key value) (push value result)) clusters)
    (sort result #'< :key #'(lambda (x) (length (car x)))))

 
Um, sorry:
 
(defun cluster-by (fn list &aux (clusters (make-hash-table)) (result nil))
     (mapcar #'(lambda (x) (push x (gethash (funcall fn x) clusters))) list)
     (maphash  #'(lambda (key value) (push value result)) clusters)
     (sort result #'< :key #'(lambda (x) (funcall fn (car x)))))
                                          ^^^^^^^^^^

Testing:

(cluster-by #'length '("a" "b" "abc" "bc" "a" "abcd" "e" "fg"))
  ===>
(("e" "a" "b" "a") ("fg" "bc") ("abc") ("abcd"))

The items are grouped by "length" and then sorted
by "length".


newLISP

(define (group-by func lst    , (alist '()) result)
  (dolist (x lst) (ainc! alist (func x) x cons '()))
  (set 'result (sort alist (fn (a b) (< (first a) (first b)))))
  (map last result))

(group-by length '("a" "b" "abc" "bc" "a" "abcd" "e" "fg"))
  ===>
(("e" "a" "b" "a") ("fg" "bc") ("abc") ("abcd"))
 
Given:

(macro (ainc! Alist Key Value Function Deflt)
  (local (E-Message Val Func Def)
    (setq Func Function)
    (if (true? Func)
      (setq Val Value)
      (begin (setq Func +) (setq Val (or Value 1))))
    (setq Def Deflt)
    (if (= nil Def) (setq Def 0))
    (unless 
      (catch
        (setf (assoc Key Alist)
          (list ($it 0) (Func Val ($it 1))))
        'E-Message)
      (if (starts-with E-Message "ERR: no reference")
        (setf Alist (cons (list Key (Func Val Def)) Alist))
        (throw-error E-Message)))))