/**
* Helper function to transform a TrainingSet to an array of feature vectors
*/
protected function getDocumentArray(TrainingSet $documents, FeatureFactory $ff)
{
$docs = array();
foreach ($documents as $d) {
$docs[] = $ff->getFeatureArray('', $d);
}
return $docs;
}
/**
* Calculate the probability that document $d belongs to the class
* $class given a set of possible classes, a feature factory and
* the model's weights l[i]
*
* @param $classes The set of possible classes
* @param $ff The feature factory
* @param $d The document
* @param string $class A class for which we calculate the probability
* @return float The probability that document $d belongs to class $class
*/
public function P(array $classes, FeatureFactory $ff, Document $d, $class)
{
$exps = array();
foreach ($classes as $cl) {
$tmp = 0.0;
foreach ($ff->getFeatureArray($cl, $d) as $i) {
$tmp += $this->l[$i];
}
$exps[$cl] = exp($tmp);
}
return $exps[$class] / array_sum($exps);
}
/**
* Count all the features for each document. All parameters are passed
* by reference and they are filled in this function. Useful for not
* making copies of big arrays.
*
* @param FeatureFactory $ff A feature factory to create the features for each document in the set
* @param TrainingSet $tset The training set (collection of labeled documents)
* @param array $termcount_per_class The count of occurences of each feature in each class
* @param array $termcount The total count of occurences of each term
* @param array $ndocs_per_class The total number of documents per class
* @param array $voc A set of the found features
* @param integer $ndocs The number of documents
* @return void
*/
protected function countTrainingSet(FeatureFactory $ff, TrainingSet $tset, array &$termcount_per_class, array &$termcount, array &$ndocs_per_class, array &$voc, &$ndocs)
{
foreach ($tset as $tdoc) {
$ndocs++;
$c = $tdoc->getClass();
$ndocs_per_class[$c]++;
$features = $ff->getFeatureArray($c, $tdoc);
if (is_int(key($features))) {
$features = array_count_values($features);
}
foreach ($features as $f => $fcnt) {
if (!isset($voc[$f])) {
$voc[$f] = 0;
}
$termcount_per_class[$c] += $fcnt;
if (isset($termcount[$c][$f])) {
$termcount[$c][$f] += $fcnt;
} else {
$termcount[$c][$f] = $fcnt;
}
}
}
}
