presto-ml/src/main/java/io/prestosql/plugin/ml/EvaluateClassifierPredictionsStateFactory.java/GroupedEvaluateClassifierPredictionsState/getTruePositives
class GroupedEvaluateClassifierPredictionsState:        @Override
        public Map<String, Integer> getTruePositives()
        {
            if (truePositives.get(groupId) == null) {
                truePositives.set(groupId, new HashMap<>());
                memoryUsage += HASH_MAP_SIZE;
            }
            return truePositives.get(groupId);
        }