sort org mode headings by tags

sort-by-tags.el

(defun org-sort-by-tags ()
    (interactive)
    (org-sort-entries nil ?f
                      (lambda () (org-get-tags (point)))
                      (lambda (a b)
                          (let ((a (if (listp (cdr a))
                                           a
                                       (buffer-substring (car a) (cdr a))))
                                (b (if (listp (cdr b))
                                           b
                                       (buffer-substring (car b) (cdr b)))))
                              (last (cl-loop for tag-a in a
                                             for tag-b in b
                                             while (not (or (string> tag-a tag-b)
                                                            (string< tag-a tag-b)))
                                             collect (string< tag-a tag-b)))))))