presto-ml/src/main/java/io/prestosql/plugin/ml/EvaluateClassifierPredictionsAggregation.java/EvaluateClassifierPredictionsAggregation/combine
class EvaluateClassifierPredictionsAggregation:    @CombineFunction
    public static void combine(@AggregationState EvaluateClassifierPredictionsState state, @AggregationState EvaluateClassifierPredictionsState scratchState)
    {
        int size = 0;
        size += mergeMaps(state.getTruePositives(), scratchState.getTruePositives());
        size += mergeMaps(state.getFalsePositives(), scratchState.getFalsePositives());
        size += mergeMaps(state.getFalseNegatives(), scratchState.getFalseNegatives());
        state.addMemoryUsage(size);
    }