Glad to see you have persevered. You need to change the if condition to: 
if ($probability->{positive} > $probability->{negative} and
    $probability->{positive} > $probability->{neutral}) {
    print "positive: $sentence\n";
}
elsif ($probability->{negative} > $probability->{positive} and
    $probability->{negative} > $probability->{neutral}) {
    print "negative: $sentence\n";
}
elsif ($probability->{neutral} > $probability->{positive} and
    $probability->{neutral} > $probability->{negative}) {
    print "neutral: $sentence\n";
}

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In reply to Re^11: how to use Algorithm::NaiveBayes module by tangent
in thread how to use Algorithm::NaiveBayes module by agnes

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