Re: Setting a task's priority based on its subtasks priorities

[Nick Dokos <nicholas.dokos@hp.com>]

Filippo A. Salustri <salustri@ryerson.ca> wrote:

> Hi all,
> I'm looking for a little coding help.
> 
> I want to try to a task's priority automatically, based on the priorities of its subtasks.
> Specifically, I'd like to set the priority of the task to the priority of the highest-priority
> subtask.
> And I'd like that task priority to be updated (if necessary) automatically any time I change the
> priority of one of its subtasks.
> 

The basic idea in all of these situations is to use org-map-entries
from the mapping API:

     (info "(org) Using the mapping API")

to walk the entries, applying a function on each.

The function to apply on each entry is frequently a specialization
of one of the functions provided by the property API:

     (info "(org) Using the property API")

In this case, you need a function to get the priority of each entry:

(def fas/task-priority ()
     (org-entry-get (point) "PRIORITY"))

which you can then give to org-map-entries:

     (org-map-entries (function fas/task-priority) t 'tree)

The assumption here is that we are at the head node and we have
an arbitrary number of subnodes. The call above will accumulate
the priorities of each subnode in a list (if a subnode does not
have a priority assigned, the priority will be nil).

For example, applying 

* section
** [#B] subsection
*** [#C] subsubsection
**** paragraph
***** [#B] subparagraph

will return the list 

(nil "B" "C" nil "B")

It is then just a matter of finding the highest priority and applying
it to the top node. Assuming that "A" is higher priority than "B" etc,
something like this will do:

--8<---------------cut here---------------start------------->8---
(defun fas/task-priority ()
  (org-entry-get (point) "PRIORITY"))

(defun fas/set-task-priority ()
  (interactive)
  (let* ((priorities (org-map-entries (function fas/task-priority) t 'tree))
	 (sortedpriorities (sort (delq nil priorities) (function string-lessp))))
    (if sortedpriorities
	(org-priority (aref (car sortedpriorities) 0)))))
--8<---------------cut here---------------end--------------->8---

org-priority wants a character, but sortedpriorities is a list of
strings, hence the aref rigmarole. It should work even if *no*
priorities are set at all: sortedpriorities will be nil, so nothing will
be done.

Nick