Filtering org tasks

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I want to be able to easily see a list of tasks that are relevant to the currently loaded desktop file. As I use desktop.el as a kind of project system, this means I only want the tasks for the project I'm currently working on.

First I wrote the tagify function, because org-mode tags can't contain . or - characters (among others I'm sure, but these are the only ones that have caused me any trouble so far). It's a simple string replacement:

(defun tagify (str)
  "Remove dots, replace - with _ in STR."
  (replace-regexp-in-string
   "-" "_" (replace-regexp-in-string "\\." "" (downcase str))))

Then I wrote a function to filter the task list by not showing anything that wasn't tagged with the name of the currently loaded desktop, unless it isn't tagged at all or no desktop has been loaded. And set this function to be the value of org-agenda-before-sorting-filter-function.

(defun filter-by-desktop (entry)
  "Return ENTRY if it has no tags or a tag corresponding to the desktop."
  (require 'desktop)
  (let ((label (when desktop-dirname
                 (tagify (file-name-base
                          (directory-file-name
                           (expand-file-name desktop-dirname))))))
        (tags (get-text-property 0 'tags entry)))
    (when (or (null desktop-dirname) (null tags) (member label tags))
      entry)))

(setq org-agenda-before-sorting-filter-function #'filter-by-desktop)

This works fine. I keep untagged tasks in the list as well because they might be important at all times and I don't want them falling through the cracks. I also want a complete list if no desktop has been loaded so I can browse through my tasks and decide what I'm going to do next.

The downside of this solution is that I have to close my current project in order to see the whole list.

Then I discovered the / key in the agenda buffer. I can't believe I didn't notice this key before. Anyway, that changed my solution.

Instead of setting org-agenda-before-sorting-filter-function I add a hook to the org-agenda-finalize-hook. The filter-by-desktop function looks a little different now:

(defun org-init-filter-by-desktop ()
  "Filter agenda by current label."
  (when desktop-dirname
    (let ((label (tagify (file-name-base
                          (directory-file-name
                           (expand-file-name desktop-dirname))))))
      (org-agenda-filter-apply (cons label nil) 'tag))))

(add-hook 'org-agenda-finalize-hook 'org-init-filter-by-desktop)

I don't need to compare any tags now, and if I want to see my entire list of tasks I can easily just press / /. Since it is easier to get back to the overview of my tasks it also doesn't bother me so much that this way any untagged tasks don't show up in the filtered buffer.

I haven't stopped using / since I discovered it. Filtering in this way is one of the things I like about ibuffer as well, now for org-mode it works excellently as well.