Re: Any faster way to find frequency of words?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Jean Louis <bugs@gnu.support> writes:

> * Eric Abrahamsen <eric@ericabrahamsen.net> [2021-05-09 17:57]:
>> Jean Louis <bugs@gnu.support> writes:
>> 
>> > I am interested if there is some better way for Emacs Lisp to find
>> > frequency of words.
>> >
>> > Purpose is to create HTML clickable tag clouds similar to image tag
>> > clouds. But I will invoke Perl from Emacs to generate it. For that, I
>> > have to analyze the text first.
>> 
>> Is there any particular improvement you're trying to make?
>
> I am invoking Perl on the fly and producing clickable HTML tag
> cloud. It would be boring and tiresome to re-write Perl's module into
> Emacs Lisp, though useful. For now, I rather just do it on the fly.
>
> As HTML tags are created from text, I need nothing but alphabetical
> characters. Function is invoked rarely.
>
> It is also useful to generate tags for particular text, that helps me
> to curate WWW pages.

Right, but what I meant was, is there anything wrong with the
implementation you posted?

>> I guess I'd suggest using Emacs syntax parsing functions, ie
>> `forward-word' and `buffer-substring'. Then you can fine tune the
>> definition of words using the local syntax table.
>
> That is also interesting approach, it could just go over the words and
> enter them into list.

Yes, and it can help you skip garbage characters that shouldn't count as
words. Things like `(skip-syntax-forward "^w")` (meaning "skip a run of
characters that aren't word constituents") can be very useful.

>> >     (mapc (lambda (word)
>> > 	    (when (> (length word) 2)
>> > 	      (let ((word (downcase word)))
>> > 		(if (numberp (gethash word hash))
>> > 		    (puthash word (1+ (gethash word hash)) hash)
>> > 		  (puthash word 1 hash)))))
>> 
>> While hash tables are probably best for very large texts, alists are
>> nice because you can use place-setting with a default, simplifying the
>> above to:
>> 
>> (cl-incf (alist-get word frequency-alist 0 nil #'equal))
>
> The idea gave me idea to use the defaults from hashes, so I have made
> it now as below (puthash word (1+ (gethash word hash 0)) hash), that
> is result of brain storming here...

> (defun rcd-word-frequency (text &optional length)
>   "Returns word frequency as hash from TEXT.
>
> Words smaller than LENGTH are discarded from counting."
>   (let* ((hash (make-hash-table :test 'equal))
> 	 (text (text-alphabetic-only text))
> 	 (length (or length 3))
> 	 (words (split-string text " " t " "))
> 	 (words (mapcar 'downcase words))
> 	 (words (mapcar (lambda (word) (when (> (length word) length) word)) words))
> 	 (words (delq nil words)))
>     (mapc (lambda (word)
> 	    (puthash word (1+ (gethash word hash 0)) hash))

I totally forgot that `gethash' has a default argument! So the line
above can just be:

(cl-incf (gethash word hash 0))

I don't know why, but I really enjoy that.

> 	  words)
>     hash))
>
> I am not sure if I should rather collect it into alist. Maybe I could
> collect it straight into by frequency ordered list like:
>
> (("word" 9) ("another" 7) ("more" 3))
>
> That is what I am doing here, to construct string of most frequent tags:
>
> (defun rcd-word-frequency-string (text &optional length how-many-words)
>   (let* ((words (rcd-word-frequency text length))
> 	 (words (hash-to-list words))
> 	 (number (or how-many-words 20))
> 	 (frequent (seq-sort (lambda (a b)
> 			       (> (cadr a) (cadr b)))
> 			     words)))
>     (mapconcat (lambda (a) (car a)) (butlast frequent (- (length frequent) number)) " ")))

I don't have a `hash-to-list' function, but once you've built your table
it seems like the rest of it is fairly straightforward.