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AI::Categorizer::FeatuUserlContributedtPerliDor::FeatureSelector::ChiSquare(3)

NAME
       AI::Categorizer::FeatureSelector::ChiSquare - ChiSquare Feature
       Selection class

SYNOPSIS
	# 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...
	  );

DESCRIPTION
       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)

METHODS
AUTHOR
       Francois	Paradis, paradifr@iro.umontreal.ca with	inspiration from Ken
       Williams	AI::Categorizer	code

perl v5.32.0			AI::Categorizer::FeatureSelector::ChiSquare(3)

NAME | SYNOPSIS | DESCRIPTION | METHODS | AUTHOR

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