Java Stream Convert List to Map of Integer-Set

Question

I have a List<StructureA>.

Now this structure comprises of a Type: typeA & typeB. Type here is an Enum.

StructureA comprises of fields : countryCode, Type, timeZone. StructureB comprises of fields: countryCode, timeZone

I want to convert this List into a Map<Type, Set<StructureB>>. Is this possible using streams?

StructureA has multiple attributes e.g. timeZone, countryCode, type etc. Type here is an enum, which can either be typeA or typeB. — Sanchay
– Sanchay, Commented May 13, 2019 at 10:41

Adrian · Accepted Answer · 2019-05-13 10:47:52Z

2

use grouping by collector

Map<Type, Set<StructureB>> collect = list.stream()
            .collect(Collectors.groupingBy(StructureA::getType,
                Collectors.mapping(a -> new StructureB(a), Collectors.toSet())));

edited May 13, 2019 at 10:47

answered May 13, 2019 at 10:41

Adrian

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