Part 2: Counting Words

emacs elisp org

This post is part of a series.

I often use an separate (Org) file to develop written content, especially when I am filling out an application that has essay questions. The answers often have a word-count or character-count limit. Let’s use Emacs and Org to count words!

Exploring Existing Functionality

First, I use builtin documentation (and tab completion) to compile some useful functions. Actually, I flailed a lot and bugged my friend who knows a bunch about Emacs and Org.

The count-words function is obviously a good place to start. The documentation indicates that functions works on either a region or buffer and that it acts differently if called from lisp (rather than interactively). I don’t know anything about regions, but the Emacs Lisp documentation for “The Region” mentions two more useful functions: region-beginning and region-end.

Looking through all the Org functions, two stick out: org-mark-subtree and org-babel-mark-block. These functions create a region on a specified chunk of Org content.

Finally, I’ll need to go to the Org location to mark the region. There are a few functions that look good for that: org-goto (though that seems to be very interactive) and org-id-goto. Also, I come across org-babel-goto-named-src-block. I already know how to name a source block. For the other go-tos, making an Org ID is easy enough: org-id-get-create. (Note, although org-id-new looks promising, I eventually learn that it doesn’t do what I want).

Marking and Counting

I need to create an Org section for each answer that I want to word count. I can either use a header/node/subtree or a source block (of text). In the first case, I’ll add a unique ID to the header (by invoking the org-id-get-create) so I can use the org-id-goto. In the source block case, I can simply give it a name.

** Describe Blah (100 words)
:PROPERTIES:
:ID:       460D55A4-7C61-485C-8778-075406BAE8A4
:END:

My answer is that blah.
#+NAME: question1
#+BEGIN_SRC text
Blah blah blah.
#+END_SRC

The snippet for counting words in a subtree looks something like:

#+NAME: subtree-method
#+BEGIN_SRC elisp
(org-id-goto "460D55A4-7C61-485C-8778-075406BAE8A4")
(org-mark-subtree)
(count-words (region-beginning) (region-end))
;; note that this snippet does not work
#+END_SRC

Unfortunately, the first snippet doesn’t work. Instead, it shows the error “Wrong type argument: markerp nil”.

Let’s try the source block way:

#+NAME: src-block-method
#+BEGIN_SRC elisp
(org-babel-goto-named-src-block "question1")
(org-babel-mark-block)
(count-words (region-beginning) (region-end))
#+END_SRC

Huzzah! This one works. Strangely, the result appears below the question block, not where I would expect it (below the code snippet).

Jaunting

My friend (who actually reads books) shows me an awesome Emacs lisp function6:

save-excursion: Save point, and current buffer; execute BODY; restore those things.

Turns out, this function is all over a bunch of e-lisp code. Let’s try it! First, the subtree version of counting words:

#+NAME: subtree-method
#+BEGIN_SRC elisp
(save-excursion
  (org-id-goto "460D55A4-7C61-485C-8778-075406BAE8A4")
  (org-mark-subtree)
  (count-words (region-beginning) (region-end)))
#+END_SRC

Low and behold! It suddenly works. Plus, the results appear below the current code block. Using save-excursion also fixes the source block method, making the results block appear near it.

One remaining issue with the subtree method is that it counts the Org properties drawer in the word count.

Count All the Things!

Finally, our word counting snippet should work on a bunch of subtrees or blocks. Let’s pass some input to the snippets. Also, we should pretty print the results. Finally, I’ve included the code to count the characters as well. The source block method ends up looking like:

#+NAME: questions
- question1
- question2
- question3

#+BEGIN_SRC elisp :var blks=questions  :results output
(save-excursion
  (while blks
    (setq b (car (car blks)))
    (setq blks (cdr blks))
    (org-babel-goto-named-src-block b)
    (org-babel-mark-block)
    (princ b)
    (princ "\t")
    (princ (count-words (region-beginning) (region-end)))
    (princ " words\t")
    (princ (- (region-end) (region-beginning)))
    (princ " chars\n")))
#+END_SRC

#+RESULTS:
: question1	3 words	16 chars
: question2	3 words	16 chars
: question3	3 words	16 chars

The same can be done for the subtree method, but with IDs as the input.

Footnotes

6 Documentation for Emacs Lisp save-excursion

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