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Can I convert List <V> to Map <K, List <V>> without foreach?

I have a list of objects. Each object has a "date" property, and I need to convert this list to a map where the key is "date" and the value is "List of objects".

I can do this using a standard foreach, but is it possible with Java 8 and streams?

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2 answers


What's collect

with groupingBy

for:



Map<K, List<V>> groups = listOfVs.stream().collect(Collectors.groupingBy(V::getK));
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You can use the API Stream

since Java 8 to group items in List

by date and put them in Map

like this:



Map<Date, List<YourObject>> collisions = yourObjectsList.stream().collect(Collectors.groupingBy(YourObject::getDate));
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