From:	Alan Gibson	Date:	Wed May 23 20:24:18 2007
Subject:	Re: how to do feature selection

im not sure if this pertains to your problem exactly, but you probably
want to specify the weighting method like

my $k = AI::Categorizer::KnowledgeSet->new( verbose => 1 ,
    features_kept = 5000,
    tfidf_weighting=>'nfc'
);

the default weighting is 'xxx' which if i understand correctly doesnt
actually do anything.

alan