TextAnalysis\Indexes\Builders\CollectionInvertedIndexBuilder::buildIndex PHP Method

    protected function buildIndex()
    {
        //first pass compute frequencies and all the terms in the collection
        foreach ($this->collection as $id => $document) {
            $freqDist = new FreqDist($document->getDocumentData());
            foreach ($freqDist->getKeyValuesByFrequency() as $term => $freq) {
                if (!isset($this->index[$term])) {
                    $this->index[$term] = array(self::FREQ => 0, self::POSTINGS => array());
                }
                $this->index[$term][self::FREQ] += $freq;
                $this->index[$term][self::POSTINGS][] = $id;
            }
            $this->metadata[$id] = $document->getMetadata();
        }
    }