I don't know if there's ever going to be a foolproof way to do what you ask, since in order to match the level of discernment we humans are capable of you will have, in the end, ended up with a module capable of true language comprehension.

Probably a compromise between a full-blown human brain and some dirty matching would be some method (or several, cross-correlated) of fingerprinting the linguistic patterns. Lingua::EN::Fathom might be a good place to start, along with some Bayesian filtering scheme such as Mail::SpamTest::Bayesian. Toss a well-designed neural net in there and you might have something.

I've considered playing with this sort of thing myself -- let me know if you run with it or find something relevant that I have neglected to mention.

Matt

Well, you could (depending on the aptitude of this person) set a unique ID cookie and cross-check it with the ISP (netblock or static IP) and the User-Agent to track the fellow, but that doesn't help you right now.

Sure, you could follow mojotoad's lead and compare the text of his posts. That would make for an interesting follow-up on how you implemented the software.

I hate to give a non-Perlish answer, but did forgiveness ever cross your mind? I think if this "Slinker" slinked his or her way back to your forum, perhaps they're deserving of another chance. Even on Perl Monks, there's reincarnation.

Of course, if they do it again, give 'em hell.

John J Reiser
newrisedesigns.com

Two academics came up with a clever use of zip-based compression for doing this type of analysis. Their scheme, which they first developed to do automatic language detection, but which is also useful for determining authorship, is glossed over here.

Basically, they noted that if you had a chunk of text from some author who was unknown, but who was a member of a known set, and if you had sample texts from each author in the set, you could concatenate the unknown text with text from each author, looking for the concatenation that compressed best.

It's a clever approach, and easily implemented in Perl.

Yeah, that was the one. B.

I'll give a mod answer instead of a Perl answer. As a mod of a gaming site, I would say that it is not worth the effort. Trolls have a tendency to get bored and move on. Writing a script to compare posts? Well some of the trolls I have had were smart enough to change the way they spoke. You don't want to ban an innocent do you? In every case they either "grown up" or they moved on.

So for the amount of time you spend designing this you might find it easier to simply watch slinker, wait for the rules to be violated and then ban him. After awhile he will get bored and move on.

Then again he may change his attitude. I have seen some of the best members start out annoying pests. It is all part of the maturity thing.

In order to stop it happening again (without going through the ISP), you could try the cookie idea .. but I'm not too sure it will work. If he really wanted to, he could find the cookie.

Instead, you might consider that if he is so desparate to be a part of the community, he'd should be willing to reform. Thus I'd suggest emailing him and letting him think you've done some sort of analysis and thus you "know" its him. Tell him why he was banned in the first place and that he's on a very short leash. If this annoys him to the point where he leaves, then is it any loss? If he re-offends then consider just banning his ISP. If he switches ISP just to get into your community, then let me know what your community is: coz I figure if it's that good, then I want to be in it too!

i don't know if there is a module that does what you want, but it is relatively easy to check. i've read that even just checking the letter-pair distributions will give good indication whether a group of texts are written by the same person.

I am not a troll.

'I<space>' => 1
'<space>a' => 2
'am' => 1
'm<space>' => 1
'<space>n' => 1
'no' => 1
...
[download]

count the letter-pair distribution for a bunch of Stinker and Slinker's posts, and a bunch of other users posts. if you're lucky it will be obvious if they are truly the same person.

let us know what you find out...;)

In terms of forgiveness, banning, etc., we didn't ban him for ever, just for a few weeks. That's our policy, like a cooling-off thing. We can't set custom cookies, it's too late for that, and the ISP he uses is huge. Believe me, we've considered those tech solutions.

I'll check out the modules mentioned by mojotoad, but in the meantime I found Text::Document -- it will compute a JaccardSimilarity and a CosineSimilarity between two strings, plus giving word frequencies, but I don't know anything about what those terms mean. Can anyone enlighten me? If you compare two strings which are identical, they come out as 1. If there's no match at all, it's zero. But in the middle..?
--
“Every bit of code is either naturally related to the problem at hand, or else it's an accidental side effect of the fact that you happened to solve the problem using a digital computer.” M-J D

http://www.google.com/search?q=letter-pair%20analysis%20author%20determine&sourceid=opera&num=0&ie=utf-8&oe=utf-8 turned up some usefull stuff. http://www.math.toronto.edu/dkhmelev/PAPERS/published/llc/khmelev.html

Another way to uniquely ID him or her is to put a GUID in the query string that is passed on every request. May or may not be easy to set up. Can be obscured (no tampering) and not as easily removed (there's a button in most browsers to "remove cookies").

This just occurred to me after seeing that zengargoyle uses Opera (see link above).

John J Reiser
newrisedesigns.com

It's not that I don't appreciate the effort, but I'm going to have to ask people to stop trying to help me with the social and administrative aspects of my problem, really.

I won't explain the rules of the community involved, that would be silly. But if we were convinced that the two people were the same, action would be taken, that's all you need to know.

If a text-analysis tool proved that the two had very similar writing styles, on a level where it was 1000-to-one that it was coincidental, then that would be considered proof.

But, having used the Fathom module, see above, I've got nothing conclusive, I'm afraid. It's a very useful tool but hasn't proven or disproven anything. There are fewer differences between two randomly-chosen posters than between Slinker and Stinker, it turns out.

Another angle of attack on this problem, which I hadn't thought of before, is mis-spellings -- Slinker has spelt "happening" as "happenning" twice, but Stinker gets it right every time...
--
“Every bit of code is either naturally related to the problem at hand, or else it's an accidental side effect of the fact that you happened to solve the problem using a digital computer.” M-J D

This is a great idea for such a problem as yours. Combining readability, tupples, fathom etc, with misspellings (or is it mispellings or missspellings or ...) I wonder how successful we could get a module for comparing two texts. I might take a look at that sometime in the next few weeks. I really think that misspellings might be a great key to comparing two texts. Judging from the above information, I'd have to guess that stinker != slinker. It would be unusually difficult to fix spellings just to get back into a web-community. (IMHO)

I am not fighting against you (I am 100% sincere), but did you realize that, actually you are not trying to find a "good" tool, but trying to find a tool to "conclusively" satisfy your guess, and to convince your community members and yourself to "believe" something you already pre-determined.

No good tool goes against your guess, would be a good tool in this situation.

I am just telling the truth, although it might be difficult to ... ;-)

But, having used the Fathom module, see above, I've got nothing conclusive, I'm afraid. It's a very useful tool but hasn't proven or disproven anything. There are fewer differences between two randomly-chosen posters than between Slinker and Stinker, it turns out.

Another angle of attack on this problem, which I hadn't thought of before, is mis-spellings -- Slinker has spelt "happening" as "happenning" twice, but Stinker gets it right every time...

Leaving alone the issue of whether it is really worth it to spend a lot of time on this mystery, testing services have dealt with some aspects of your problem. Especially the personality tests where they ask you the same question in many slightly different ways and perform some kind of analysis to determine whether you are trying to spoof the test by appearing to be someone you are not.

Your mention of a spelling discrepency brought to mind a scene from The Princess Bride where Westley was to add poison to one of the drinks, and his adversary was to choose, after Westley had shifted (or not) the position of the glasses. The bad guy goes through a series of qustions and answers trying to figure out Westley's thoughts -- "You placed the poisoned glass closer to me so I'd choose it. But I'm too smart for that, so it must be the one closest to you... But you knew I'd anticipate that move, so it must be the one closest to me after all." And so on for a few minutes or pretty funny dialogue. (I'm sure I got the details turned around, but you get the gist)

Is this guy deliberately mispelling a word or two just to throw you off? Does it really matter? It still boils down to a guess, doesn't it?

Even after centuries of linguistic analysis, and lately with some fairly sophisticated computer analysis, scholars are still arguing whether Marlowe wrote the works attributed to Shakespeare, or whether Shakespeare was, indeed, Shakespeare.

-----
"Computeri non cogitant, ergo non sunt"

The statistical measures still won't prove Slinker is Stinker, however.

-Mark

As an alternative to that (and I think the compression alternative is very cool too) I'd consider a mathematical analysis of compiled information on visitor behavior between two suspected identities. Variables to analyze could include:

Just a few ideas among many. In situations such as yours, I couldn't justify throwing so much effort away on garbage like this troll, but I'd try to K.I.S.S. as much as possible. It's more fun to foil with less force. That's why Perl is so cool, and so endearing to the lazy punmiester who'd like to brag (hubris) about how easy it was to triumphantly trounce the troll.

--
Tommy Butler, a.k.a. TOMMY