"Text Classification using Text Plugin - NaiveBayes, Updateable Models"

pser

This post refers to http://rapid-i.com/rapidforum/index.php/topic,368.0.html and http://rapid-i.com/rapidforum/index.php/topic,369.0.html. It adresses the problems I experienced when trying to update models.

Given I created a wordlist and saved it to disk. Then I can use StringTextInput several times, each time loading and vectorizing only a part of the database texts. I want to give the word vectors to a learner that learns to classify texts. It should be a learner that produces an updatable model. I tried NaiveBayes.

Problem 5: The UpdateModel Operator throws an error that says the corresponding model (which is a DistributionModel) is not updatable. Adding the line "public boolean isUpdatable() { return true; }" to the DistributionModel.java solved the problem. I did not find any learner/model that worked with UpdateModel without modifying the sourcecode. Did I do something wrong?

Problem 6: NaiveBayes does not work properly on my examples. It classifies all texts with the same class. I looked into the sourcecode and I think the problem is that NaiveBayes multiplies all probabilities (when handling numerical attributes). Since I used about 1600 attributes the product was probably too small for a double and was rounded to 0.

I decided to use some Bayes Operator from Weka which computes probabilities in terms of sums of logarithms instead. Again I get the problem with UpdateModel, I haven't tried if the same fix as mentiond above works again.

TobiasMalbrecht

Hi,

pser wrote:
Problem 5: The UpdateModel Operator throws an error that says the corresponding model (which is a DistributionModel) is not updatable. Adding the line "public boolean isUpdatable() { return true; }" to the DistributionModel.java solved the problem. I did not find any learner/model that worked with UpdateModel without modifying the sourcecode. Did I do something wrong?

No, as far as I know the naive bayes model is the only updatable model at the moment. Unfortunately we forget to mark it as updatable by adding the appropriate method. We will add the method [tt]isUpdatable()[/tt].

pser wrote:

Problem 6: NaiveBayes does not work properly on my examples. It classifies all texts with the same class. I looked into the sourcecode and I think the problem is that NaiveBayes multiplies all probabilities (when handling numerical attributes). Since I used about 1600 attributes the product was probably too small for a double and was rounded to 0. I decided to use some Bayes Operator from Weka which computes probabilities in terms of sums of logarithms instead. Again I get the problem with UpdateModel, I haven't tried if the same fix as mentiond above works again.

I don't know whether the problem is that the probabilities are too small, but it may be. Did you check the learners already without the [tt]ModelUpdater[/tt] but the [tt]ModelApplier[/tt]?

Regards,
Tobias