Re: regexp filter to match non-english characters

[Michal Nazarewicz]

Ted Zlatanov <tzz@lifelogs.com> writes:

> On Wed, 05 Nov 2008 14:14:31 -0600 "Robert D. Crawford" <rdc1x@comcast.net> 
> wrote:
>
> RDC> Ted Zlatanov <tzz@lifelogs.com> writes:
>>> (string-match "[^\\000-\\1ff]" "hello")   ;; OK
>>> 
>>> This will match character values over 0x1FF, which is the limit of
>>> extended ASCII.  Does that work for you?
>
> RDC> Will this match the unicode double ">" and the like?  Some people
> RDC> feel the need to use these in their breadcrumbs and such.  If
> RDC> there is no way to just filter out the foreign characters, I will
> RDC> use it.
>
> You can just try it!
>
> (string-match "[^\\000-\\1ff]" "»") ;; returns 0, meaning it's a match
> (string-match "[^\\000-\\1ff]" ">>") ;; returns nil, meaning it's not a match
>
> RDC> The other possibility is to lower permanently on each character that is
> RDC> read to me, but this seems tedious and time consuming on my part and
> RDC> likely slow for gnus to score.
>
> Nah, the above should work.  You will need a single backslash instead of
> two, though (the doubling is needed to tell Emacs Lisp that's a real
> backslash inside the string when it reads it in).

"<<" and ">>" have codes U+00AB and U+00BB so that's why they match but
there are plenty of other characters which may show up in an English
text, like (I'll use a (sequence of) ASCII characters which resembles
the proper unicode character) "`" (U+2018), "'" (U+2019), "``" (U+201C)
, "''" (U+201D) or "..." (U+2026) which will cause the entry to be
filtered out.

Besides, I think what you really meant was:

(string-match "[^\\0-\\177]" "string") 

since "1ff" is not a valid octal number.


I think that taking the title of the entry and checking if at least 90%
are ASCII characters would be sufficient to filter out Asian texts.  You
can also try taking first 100 (or so) characters of the body.  I think
you could use replace-regexp-in-string for that purpose:

(defun mn-non-english-p (string) 
  (>
   (* (length (replace-regexp-in-string "[^\\0-\\77]" "" string)) 10)
   (* (length string) 9)))

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