How can I make an emacs command M-x sum-the-brackets that scans highlighted text for all occurrences of [ <number> u ] and [ <number>u ], and sums them?


Selecting the text

Here is some text. [0.1u]
Here is some more text [0.2 u]
And here is some noise: 0.2

and running M-x sum-the-brackets should yield 0.3 in the mini-buffer.


3 Answers 3


You want to search for all instances of the regular expression \[ *\([-0-9.]+\) *u *\]:

(re-search-forward "\\[ *\\([-0-9.]+\\) *u *\\]" nil t)

and sum the matches:

(setq sum (+ sum (string-to-number (match-string 1))))

Since you want this to apply to the region only, you'll need to narrow-to-region and then restore the restriction using save-restriction.

Putting this all together, we get:

(defun my-sum (begin end)
  (interactive "r")
      (narrow-to-region begin end)
      (goto-char (point-min))
      (let ((sum 0))
        (while (re-search-forward "\\[ *\\([-0-9.]+\\) *u *\\]" nil t)
          (setq sum (+ sum (string-to-number (match-string 1)))))
        (message "%s" sum)

Using standard commands:

M-: (setq n 0) RET
C-M-% \[\([0-9.]+\) *u\] RET \,(prog1 \& (setq n (+ n \#1))) RET !
M-: n RET

Note: to get more information have a look at help for query-replace-regexp, prog1 and eval-expression

  • This is cool, I didn't know this replacement style is possible. I corrected your answer and made a remark about finding more help. Please review my edit to your answer.
    – jue
    Jul 11, 2017 at 9:27

Here is the function you wished for.
I put some extra variables inside this function, so it is easier for you to enhance it.

(defun sum-the-brackets (begin end)
    "sums up values in brackets with style '[ FLOAT u ]'
For non interactive use BEGIN must be smaller then END.
If FLOAT is omitted bracket counts with value one
If FLOAT is '.' it counts as value 0
Whitespace inside the brackets is ignored"
    (interactive "r")
        (let ((n 0)       ; desired value
              (c 0)       ; counter
              (tmp nil)   ; string in bracket
              (tmpf 0))   ; value of string in bracket
            (goto-char begin)
            (while (search-forward-regexp "\\[ *\\([0-9]*\\.?[0-9]*\\) *\\(u *\\)\\]" end t)
                (setq c (1+ c))
                (setq tmp (match-string 1))
                (setq tmpf (if (string= "" tmp) 1                              
                               (string-to-number tmp)))
                (setq n (+ n tmpf)))
            (message "Sum-Value: %2.3f ; brackets counted: %d" n c))))

This function sums up following 6 brackets to value 3.6:

Here is some text. [0.1u]
Here is some more text [ 0.2 u]
count me with value zero point 3 [.3 u]
count me with value two [2 u]
count me with value one [u]
count me with zero [ . u ]
And here is some noise: 0.2

Note: politza answer is way more cool. :)

Note2: comments/edits on improvement of the code are very welcome, I did code this for practice and it took me a while. :)

Edit: the user "jch" changed the question. I will not update this answer because "jch" gave an answer which fits his edits and maybe someone else finds my answer useful.

  • 1. Is narrowing really necessary ? 2. Second argument of search-forward-regexp you gave is also the default. 3. It's always nice beeing able to use a command as function as well, i.e. use (begin end) arguments and setup interactive usage in the (interactive) spec appropriately.
    – politza
    Jul 11, 2017 at 21:59
  • @politza many thanks for your constructive comment! I changed the code accordingly. Also I spotted, that the questioner wanted to evaluate [u].
    – jue
    Jul 11, 2017 at 23:55
  • The apparent [u] in the orignal answer was a typo, due to some misquoted markup. I merely fixed the markup, which caused the spurious [u] to disapper. As to your answer — please keep it around, it's good to have multiple solutions written in different styles.
    – jch
    Jul 13, 2017 at 18:44
  • You also wrote a good and correct answer, so there is no need to have a correct answer a second time. Besides, my original code, before my edit looks nearly the same like yours and I don't want to revert my code. Everything is fine! :)
    – jue
    Jul 13, 2017 at 18:50

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