Twi :
I have the following code which could be much simpler using Java 8 stream API:
List<List<String>> listOfListValues;
public List<String> getAsFlattenedList() {
List<String> listOfValues= new ArrayList<>();
for (List<String> value: listOfListValues) {
listOfValues.add(String.valueOf(value));
}
return listOfValues;
}
I searched for a solution on SO and found this:
listOfListValues.stream()
.flatMap(List::stream)
.collect(Collectors.toList());
But this doesn't do the same what I want.
Roland :
You require only a "simple" map
here:
List<List<String>> listOfListValues;
public List<String> getAsFlattenedList() {
return listOfListValues.stream()
.map(String::valueOf)
.collect(toList());
}
flatMap
is rather used to transform one Stream
to another, which makes sense if you need more entries or less then currently available (or just a newly mapped Stream
to filter/map/etc it further down), e.g.:
count all the unique strings of all lists:
listOfListValues.stream() .flatMap(List::stream) // we want to count all, also those from the "inner" list... .distinct() .count()
truncate entries after a certain size:
listOfListValues.stream() .flatMap(list -> { if (list.size() > 3) // in this case we use only some of the entries return Stream.concat(list.subList(0, 2).stream(), Stream.of("...")); else return list.stream(); }) .collect(Collectors.toList());
flattening values of a map for several interested keys:
Map<Key, List<Value>> map = new HashMap<>(); Stream<Value> valueStream = interestedKeys.stream() .map(map::get) .flatMap(List::stream);