Re: How to implement line sorting, uniquifying and counting function in emacs?

[Evgeny Roubinchtein <zhenya@freeshell.org>]

,----
| In shell you can do this:
|    cat file | sort | uniq -d | wc 
| 
| to count the repeated lines. You can also do
| 
|    cat file | sort | uniq -u | wc
| 
| to count the unique lines.
| 
| Sometimes I have to do this on windows platform where I do have emacs.
| This means that I cannot escape to shell and that route is not available.
| 
| Lisp has sort-lines, but no uniq -u or uniq -d available. Also I do not
| know the equivalent to wc.
`----

Assuming the text you are interested in is in a buffer, one apprach is
to use the `sort-lines' function.  Once the lines are sorted, it's
pretty easy to count unique and non-unique lines.  That's one
approach.

(defun count-repeated-lines (&optional beg end)
  (let ((buf (current-buffer))
	(repeated-count 0)
	(unique-count 0)
	(cur-line nil)
	(prev-line nil))
    (with-temp-buffer
      (insert-buffer-substring buf 
			       (and beg 
				    (with-current-buffer buf
				      (save-excursion
					(goto-char beg)
					(line-beginning-position))))  
			       end)
      (sort-lines nil (point-min) (point-max))
      ;; put a dummy line before the text to make the loop simpler
      (goto-char (point-min))
      (insert "\n")
      (goto-char (point-min))
      (while (and (zerop (forward-line 1)) (/= (point) (point-max)))
	(setq cur-line (buffer-substring-no-properties (point) 
						       (save-excursion (end-of-line) 
								       (point))))
	(if (and prev-line (string= prev-line cur-line))
	    (setq repeated-count (1+ repeated-count))
	  (setq unique-count (1+ unique-count)))
	(setq prev-line cur-line))
      (cons unique-count repeated-count))))

Instead of sorting lines, you could use Emacs built-in hash tables
(built-in as of GNU Emacs v21, not sure what version of XEmacs first
introduced hash tables) to keep track of lines you've encountered so
far.  (You also don't need a temporary buffer in that case).

(defun count-repeated-lines (&optional beg end)
  (let ((buf (current-buffer))
	(beg (or (and beg (save-excursion (goto-char beg) (line-beginning-position))) 
		 (point-min)))
	(end (or end (point-max)))
	(lines-hash (make-hash-table :test #'equal))
	(unique-count 0)
	(repeated-count 0)
	(cur-line nil))
    (save-excursion 
      (goto-char beg)
      (beginning-of-line)
      (while (< (point) end)
	(setq cur-line (buffer-substring-no-properties (point) 
						       (save-excursion (end-of-line) 
								       (point))))
	(if (gethash cur-line lines-hash)
	    (setq repeated-count (1+ repeated-count))
	  (setq unique-count (1+ unique-count))
	  (puthash cur-line t lines-hash))
	(forward-line))
      (cons unique-count repeated-count ))))