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Re: processing a large buffer contents to a hash table

From: Andreas Politz
Subject: Re: processing a large buffer contents to a hash table
Date: Fri, 09 Jan 2009 18:06:06 +0100
User-agent: Mozilla-Thunderbird (X11/20081018)

Seweryn Kokot wrote:

I'm trying to write a function in elisp which returns word frequency of
a buffer content . It works but for a large file
(around 250 000 words) it takes 15 seconds, while a similar function in python
takes 4s.
Here is the function which process a buffer word by word and write word
frequency to a hash table.
(defun word-frequency-process-buffer ()
  (let ((buffer (current-buffer)) bounds beg end word)
          (goto-char (point-min))
          (while (re-search-forward "\\<[[:word:]]+\\>" nil t)
          (word-frequency-incr (downcase (match-string 0))))))

...should do the same. (?)
More specific, I think bounds-of-thing-at-point is
your bottleneck. And try to compile everything.


;;        (while (forward-word 1)
                (setq bounds (bounds-of-thing-at-point 'word))
                (setq beg (car bounds))
                (setq end (cdr bounds))
                (setq word (downcase (buffer-substring-no-properties beg end)))
                (word-frequency-incr word)

The main function is word-frequency which operates on the current buffer
and gives *frequencies* with word statistics.

Any idea how to optimize `word-frequency-process-buffer' function?

Thanks in advance.

P.S. I took some code from command-frequency.el library

------ code start
(defvar word-frequency-table (make-hash-table :test 'equal :size 128))

(defvar word-frequency-buffer "*frequencies*"
  "Buffer where frequencies are displayed.")

(defun word-frequency-incr (word)
  (puthash word (1+ (gethash word word-frequency-table 0)) 

(defun word-frequency-list (&optional reverse limit)
  "Returns a cons which car is sum of times any word was used
and cdr is a list of (word . count) pairs.  If REVERSE is nil
sorts it starting from the most used word; if it is 'no-sort
the list is not sorted; if it is non-nil and not 'no-sort sorts
it from the least used words.  If LIMIT is positive number
only words which were used more then LIMIT times will be
added.  If it is negative number only words which were used
less then -LIMIT times will be added."
  (let (l (sum 0))
      ((or (not (numberp limit)) (= limit 0))
       (lambda (k v) (setq l (cons (cons k v) l) sum (+ sum v))))
      ((= limit -1) (lambda (k v) (setq sum (+ sum v))))
      ((< limit 0)
       (setq limit (- limit))
       (lambda (k v) (setq sum (+ sum v))
         (if (< v limit) (setq l (cons (cons k v) l)))))
       (lambda (k v) (setq sum (+ sum v))
         (if (> v limit) (setq l (cons (cons k v) l))))))
    (cons sum
           ((equal reverse 'no-sort) l)
           (reverse (sort l (lambda (a b) (< (cdr a) (cdr b)))))
           (t       (sort l (lambda (a b) (> (cdr a) (cdr b)))))))))

(defun word-frequency-string (&optional reverse limit func)
  "Returns formatted string with word usage statistics.

If FUNC is nil each line contains number of times word was
called and the word; if it is t percentage usage is added in
the middle; if it is 'raw each line will contain number an
word separated by single line (with no formatting) otherwise
FUNC must be a function returning a string which will be called
for each entry with three arguments: number of times word was
called, percentage usage and the word.

See `word-frequency-list' for description of REVERSE and LIMIT
  (let* ((list (word-frequency-list reverse)) (sum (car list)))
      ((not func) (lambda (e) (format "%7d  %s\n" (cdr e) (car e))))
      ((equal func t)
       (lambda (e) (format "%7d  %6.2f%%  %s\n"
                           (cdr e) (/ (* 1e2 (cdr e)) sum) (car e))))
      ((equal func 'raw) (lambda (e) (format "%d %s\n" (cdr e) (car e))))
      (t (lambda (e) (funcall func (cdr e) (/ (* 1e2 (cdr e)) sum) (car e)))))
     (cdr list) "")))

(defun word-frequency (&optional where reverse limit func)
  "Formats word usage statistics using
`word-frequency-string' function (see for description of
REVERSE, LIMIT and FUNC arguments) and:
- if WHERE is nil inserts it in th e
  or displays it in echo area if possible; else
- if WHERE is t inserts it in the current buffer; else
- if WHERE is an empty string inserts it into
  `word-frequency-buffer' buffer; else
- inserts it into buffer WHERE.

When called interactively behaves as if WHERE and LIMIT were nil,
FUNC was t and:
- with no prefix argument - REVERSE was nil;
- with universal or positive prefix arument - REVERSE was t;
- with negative prefix argument - REVERSE was 'no-sort."

  (interactive (list nil
                      ((not current-prefix-arg) nil)
                      ((> (prefix-numeric-value current-prefix-arg) 0))
                      (t 'no-sort))
                     nil t))
  (clrhash word-frequency-table)
   ((not where)
    (display-message-or-buffer (word-frequency-string reverse limit func)
   ((equal where t)
    (insert (word-frequency-string reverse limit func)))
     (if (and (stringp where) (string= where ""))
         word-frequency-buffer where)
     (word-frequency-string reverse limit func)))))

(defun word-frequency-process-buffer ()
  (let ((buffer (current-buffer))
          (goto-char (point-min))
          (while (re-search-forward "\\<[[:word:]]+\\>" nil t)
;;        (while (forward-word 1)
                (setq bounds (bounds-of-thing-at-point 'word))
                (setq beg (car bounds))
                (setq end (cdr bounds))
                (setq word (downcase (buffer-substring-no-properties beg end)))
                (word-frequency-incr word)
----- code end

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