Lucas T :
I'm trying to split a list into a list of list where each list has a maximum size of 4.
I would like to know how this is possible to do using lambdas.
Currently the way I'm doing it is as follow:
List<List<Object>> listOfList = new ArrayList<>();
final int MAX_ROW_LENGTH = 4;
int startIndex =0;
while(startIndex <= listToSplit.size() )
{
int endIndex = ( ( startIndex+MAX_ROW_LENGTH ) < listToSplit.size() ) ? startIndex+MAX_ROW_LENGTH : listToSplit.size();
listOfList.add(new ArrayList<>(listToSplit.subList(startIndex, endIndex)));
startIndex = startIndex+MAX_ROW_LENGTH;
}
UPDATE
It seems that there isn't a simple way to use lambdas to split lists. While all of the answers are much appreciated, they're also a wonderful example of when lambdas do not simplify things.
alex.b :
Try this approach:
static <T> List<List<T>> listSplitter(List<T> incoming, int size) {
// add validation if needed
return incoming.stream()
.collect(Collector.of(
ArrayList::new,
(accumulator, item) -> {
if(accumulator.isEmpty()) {
accumulator.add(new ArrayList<>(singletonList(item)));
} else {
List<T> last = accumulator.get(accumulator.size() - 1);
if(last.size() == size) {
accumulator.add(new ArrayList<>(singletonList(item)));
} else {
last.add(item);
}
}
},
(li1, li2) -> {
li1.addAll(li2);
return li1;
}
));
}
System.out.println(
listSplitter(
Arrays.asList(0, 1, 2, 3, 4, 5, 6, 7, 8, 9),
4
)
);
Also note that this code could be optimized, instead of:
new ArrayList<>(Collections.singletonList(item))
use this one:
List<List<T>> newList = new ArrayList<>(size);
newList.add(item);
return newList;
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