Collect values from HashMap into one array using streams api

Question

I have a map, containing strings as a key and ArrayList as values. I want to use stream api to get as a result all the Arrays from values as one array.

Map<Integer,  ArrayList<String>> map = new HashMap<>();

Result: one ArrayList<String> containing all the Strings from value arrays and preferably unique values.

of course I googled, I just did not find rights words) thanks for the link. I tried flatmap first, but I did not know that it should be List::stream inside. — Foenix
– Foenix, Commented Oct 14, 2020 at 10:28
@MyFoenix in any case, it can be done with method reference, or .flatMap(a -> a.stream()) but the method reference in this case is better — Youcef LAIDANI
– Youcef LAIDANI, Commented Oct 14, 2020 at 10:32

Youcef LAIDANI · Accepted Answer · 2020-10-14 10:14:12Z

4

Are you looking to this :

List<String> distinctValues = map.values().stream() // Stream<ArrayList<String>>
        .flatMap(List::stream)                      // Stream<String>
        .distinct()
        .collect(Collectors.toList());

If you prefer ArrayList as a result, then use :

        .collect(Collectors.toCollection(ArrayList::new));

answered Oct 14, 2020 at 10:14

Youcef LAIDANI

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