Org mode how to sort entries

Question

In an Org-mode document, let's imagine that my entries are following this pattern:

* TODO Note page 2 [0/1]
  my notes, must be at second position after sorting
  - [ ] todo 1

* Note page 14                                                        :A_Tag:
  my notes, must be at third position after sorting

* Note page 1
  my notes, must be at first position after sorting

Question: how to sort these entries according to page number?

Expected result is:

* Note page 1
  my notes, must be at first position after sorting 

* TODO Note page 2 [0/1]
  my notes, must be at second position after sorting
  - [ ] todo 1

* Note page 14                                                        :A_Tag:
  my notes, must be at third position after sorting

I know the function org-sort-entries but AFAIK we can not use it with default options. We must define that the sort must be performed according to a pattern like

^* <ignore TODO> Note page [Number] <ignore tag list>$

For instance, if I use org-sort-entries + [a] I get:

* Note page 1
  my notes, must be at first position after sorting

* Note page 14                                                        :A_Tag:
  my notes, must be at second position after sorting

* TODO Note page 2 [0/1]
  my notes, must be at third position after sorting
  - [ ] todo 1

I get an alphabetically sorted output, however, this is not what I want to do. What is the right way to do that?

----- update

with your function org-page-sort I get:

* Note page 1
  my notes, must be at first position after sorting* TODO Note page 2 [0/1]
  my notes, must be at second position after sorting
  - [ ] todo 1

* Note page 14                                                        :A_Tag:
  my notes, must be at third position after sorting

maybe a little bug. However, I do not see where is the problem as your function prints

looking at page Note page 2 [0/1]
looking at page Note page 14
looking at page Note page 1

as expected.

Anyway thank you very much (I upvoted your answer), this is the kind of solution I was looking for!

Answer 1

You need to define a custom function to get the key for sorting. Then you can tell org-sort-entries to use the function. Below I use a regex to get the page number and convert it to a number (it starts out as a string).

(defun org-page-sort ()
  (interactive)
  (mark-whole-buffer)
  (org-sort-entries
   nil ?f
   (lambda ()
     (let ((heading (nth 4 (org-heading-components))))
       (if (string-match "page \\([0-9]+\\)" heading)
           (string-to-number (match-string 1 heading))
         1)))))