AI::Categorizer::FeatureSelector::ChiSquare - ChiSquare Feature Selection class
# the recommended way to use this class is to let the KnowledgeSet # instanciate it use AI::Categorizer::KnowledgeSetSMART; my $ksetCHI = new AI::Categorizer::KnowledgeSetSMART( tfidf_notation =>'Categorizer', feature_selection=>'chi_square', ...other parameters...); # however it is also possible to pass an instance to the KnowledgeSet use AI::Categorizer::KnowledgeSet; use AI::Categorizer::FeatureSelector::ChiSquare; my $ksetCHI = new AI::Categorizer::KnowledgeSet( feature_selector => new ChiSquare(features_kept=>2000,verbose=>1), ...other parameters... );
Feature selection with the ChiSquare function.
Chi-Square(t,ci) = (N.(AD-CB)^2) ----------------------- (A+C).(B+D).(A+B).(C+D)
where t = term ci = category i N = number of documents in the collection A = number of times where t and c co-occur B = " " " t occurs without c C = " " " c occurs without t D = " " " neither c nor t occur
for more details, see : Yiming Yang, Jan O. Pedersen, A Comparative Study on Feature Selection in Text Categorization, in Proceedings of ICML-97, 14th International Conference on Machine Learning, 1997. (available on citeseer.nj.nec.com)
Francois Paradis, firstname.lastname@example.org with inspiration from Ken Williams AI::Categorizer code