Java 8 partition list

Question

Is it possible to partition a List in pure Jdk8 into equal chunks (sublists).

I know it is possible using Guava Lists class, but can we do it with pure Jdk? I don't want to add new jars to my project, just for one use case.

SOLUTONS:

The best solution till now was presented by tagir-valeev:

I have also found three other possibilities, but they are ment for only few cases:

1.Collectors.partitioningBy() to split the list into 2 sublists – as follows:

intList.stream().collect(Collectors.partitioningBy(s -> s > 6));     List<List<Integer>> subSets = new ArrayList<List<Integer>>(groups.values()); 

2.Collectors.groupingBy() to split our list to multiple partitions:

 Map<Integer, List<Integer>> groups =        intList.stream().collect(Collectors.groupingBy(s -> (s - 1) / 3));     List<List<Integer>> subSets = new ArrayList<List<Integer>>(groups.values()); 

3.Split by separator:

List<Integer> intList = Lists.newArrayList(1, 2, 3, 0, 4, 5, 6, 0, 7, 8);      int[] indexes =        Stream.of(IntStream.of(-1), IntStream.range(0, intList.size())       .filter(i -> intList.get(i) == 0), IntStream.of(intList.size()))       .flatMapToInt(s -> s).toArray();     List<List<Integer>> subSets =        IntStream.range(0, indexes.length - 1)                .mapToObj(i -> intList.subList(indexes[i] + 1, indexes[i + 1]))                .collect(Collectors.toList()); 

4.Using Streams + counter source:

final List<Integer> numbers = Arrays.asList(1,2,3,4,5,6,7); final int chunkSize = 3; final AtomicInteger counter = new AtomicInteger();  final Collection<List<Integer>> result = numbers.stream()     .collect(Collectors.groupingBy(it -> counter.getAndIncrement() / chunkSize))     .values(); 

Answer 1

That can be done easily using the subList() method:

List<String> collection = new ArrayList<>(21); // fill collection int chunkSize = 10; List<List<String>> lists = new ArrayList<>(); for (int i = 0; i < collection.size(); i += chunkSize) {     int end = Math.min(collection.size(), i + chunkSize);     lists.add(collection.subList(i, end)); } 

Answer 2

Try using this code, it uses Java 8:

public static Collection<List<Integer>> splitListBySize(List<Integer> intList, int size) {      if (!intList.isEmpty() && size > 0) {         final AtomicInteger counter = new AtomicInteger(0);         return intList.stream().collect(Collectors.groupingBy(it -> counter.getAndIncrement() / size)).values();     }     return null; }