CREATE OR REPLACE FUNCTION docs_within_distance(vec topics, threshold float)
RETURNS TABLE(doc_id int, distance float) AS $$
BEGIN
	RETURN QUERY
    SELECT *
    FROM (SELECT id, (SELECT sum(vec[i] * ln(vec[i] / topics[i]))
                      FROM generate_subscripts(topics, 1) AS i
                      WHERE topics[i] > 0) AS distance
          FROM doc) AS tab
    WHERE tab.distance < threshold
    ORDER BY tab.distance;
END;
$$ LANGUAGE plpgsql;