What is the Java equivalent of Numpy's array_split? [duplicate]

If it helps anyone.

@Test public void testListPartition() { // Given Integer[] is = new Integer[] {7, 3, 9, 10, 5, 6, 8, 13}; List<Integer> isList = new ArrayList<Integer>(); Collections.addAll(isList, is); int nThreads = 3; int sizeSublist = (int) Math.ceil(isList.size()/(double)nThreads); List<Integer> truthOne = new ArrayList<Integer>(); Collections.addAll(truthOne, new Integer[] {7, 3, 9}); List<Integer> truthTwo = new ArrayList<Integer>(); Collections.addAll(truthTwo, new Integer[] {10, 5, 6}); List<Integer> truthThree = new ArrayList<Integer>(); Collections.addAll(truthThree, new Integer[] {8, 13}); // When List<List<Integer>> partitions = Lists.partition(isList, sizeSublist); // Then assertEquals(truthOne, partitions.get(0)); assertEquals(truthTwo, partitions.get(1)); assertEquals(truthThree, partitions.get(2)); } 

You can split the list using Stream.

static <T> List<List<T>> splitList(List<T> list, int n) { int size = list.size(); return IntStream.range(0, (size + n - 1) / n) .map(i -> n * i) .mapToObj(i -> list.subList(i, Math.min(i + n, size))) .collect(Collectors.toList()); } 

Note that since this uses subList(), each split list shares the original list.

You can split the array as well.

@SuppressWarnings("unchecked") static <T> T[][] splitArray(T[] array, int n) { int size = array.length; return IntStream.range(0, (size + n - 1) / n) .map(i -> n * i) .mapToObj(i -> Arrays.copyOfRange(array, i, Math.min(i + n, size))) .toArray(i -> (T[][])Array.newInstance(array.getClass(), n)); } 

However, this cannot be applied to arrays of primitive types.

Separate implementations are required for primitive types.

For example, for int array:

static int[][] splitArray(int[] array, int n) { int size = array.length; return IntStream.range(0, (size + n - 1) / n) .map(i -> n * i) .mapToObj(i -> Arrays.copyOfRange(array, i, Math.min(i + n, size))) .toArray(int[][]::new); } 

test:

public static void main(String[] args) { List<Integer> list = List.of(7, 3, 9, 10, 5, 6, 8, 13); System.out.println(splitList(list, 3)); Integer[] array = {7, 3, 9, 10, 5, 6, 8, 13}; System.out.println(Arrays.deepToString(splitArray(array, 3))); int[] ints = {7, 3, 9, 10, 5, 6, 8, 13}; System.out.println(Arrays.deepToString(splitArray(ints, 3))); } 

output:

[[7, 3, 9], [10, 5, 6], [8, 13]] [[7, 3, 9], [10, 5, 6], [8, 13]] [[7, 3, 9], [10, 5, 6], [8, 13]]