[SOLVED]: Re: Is there any existing solution to move list number backwards, forwards in a list?

[Jean Louis <bugs@gnu.support>]

* Jean Louis <bugs@gnu.support> [2022-10-21 11:50]:
> For purposes of changing priorities of objects in a set, I need to
> move single item in a list backwards and forwards.
> 
> Let us say item is number 7 in following list:
> 
> '(1 2 3 4 5 6 7 8 9)
> 
> Then I wish to move item number 7 to different number and renumber all
> items so that number 7 becomes number 6 and number 6 comes in the
> place of number 7.
> 
> Situation is more complex, each object ID has its priority like one of
> those in the list. So each object ID has to be updated with its
> priority when I press single click.
> 
> As it looks somehow common to me, maybe somebody knows if something
> like that exists as a package.

My request is complicated to understand. And I have made function
which works, though it is slow as it has to update all the objects
with new priority. Priorities could be anything like '(3 4 5) so how
to update object with priority 4 to be before 3? Without adding some
numbers it does not work. I have chosen to multiply items by 10, like
'(30 40 50), then object's priority 40 can by decreased for 15 and get
priority 25, or increased for 15 and get priority 55, this way
priorities are solved. It is now up to me to speed it up by using only
one SQL statement.

(defun hyperscope-hyperdocument-set-priority (hyperscope-set id direction)
  (let* ((hyperdocuments (rcd-sql-list (cond (hyperscope-set "SELECT hyobjects_id FROM hyobjects
                                                               WHERE hyobjects_parent = $1
                                                            ORDER BY hyobjects_priorities, hyobjects_id")
					     (t "SELECT hyobjects_id FROM hyobjects
                                                  WHERE hyobjects_parent = NULL
                                               ORDER BY hyobjects_priorities, hyobjects_id"))
                        	       cf-db hyperscope-set))
	 (hash (make-hash-table :test #'equal))
	 (renumbered (let ((count 20))
		       (mapcar (lambda (id)
				 (puthash id (* (setq count (1+ count)) 10) hash))
			       hyperdocuments))))
    (cond ((eq direction 'back) (puthash id (- (gethash id hash) 15) hash))
	  ((eq direction 'forth) (puthash id (+ (gethash id hash) 15) hash))
	  (t (error "Verify arguments to `hyperscope-hyperdocument-set-priority'")))
    (let ((keys (hash-table-keys hash)))
      (while keys
	(let ((key (pop keys)))
	(hlink-update-priority-1 key (gethash key hash)))))))

-- 
Jean

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