presto-main/src/main/java/io/prestosql/sql/planner/plan/StatisticAggregationsDescriptor.java/StatisticAggregationsDescriptor/map
class StatisticAggregationsDescriptor:    private static <K, V1, V2> Map<K, V2> map(Map<K, V1> input, Function<V1, V2> mapper)
    {
        return input.entrySet()
                .stream()
                .collect(toImmutableMap(Map.Entry::getKey, entry -> mapper.apply(entry.getValue())));
    }