如何将一个数组列表(size=1000)拆分为多个相同大小(=10)的数组列表?

ArrayList<Integer> results;

当前回答

    **Divide a list to lists of n size**

    import java.util.AbstractList;
    import java.util.ArrayList;
    import java.util.List;

    public final class PartitionUtil<T> extends AbstractList<List<T>> {

        private final List<T> list;
        private final int chunkSize;

        private PartitionUtil(List<T> list, int chunkSize) {
            this.list = new ArrayList<>(list);
            this.chunkSize = chunkSize;
        }

        public static <T> PartitionUtil<T> ofSize(List<T> list, int chunkSize) {
            return new PartitionUtil<>(list, chunkSize);
        }

        @Override
        public List<T> get(int index) {
            int start = index * chunkSize;
            int end = Math.min(start + chunkSize, list.size());

            if (start > end) {
                throw new IndexOutOfBoundsException("Index " + index + " is out of the list range <0," + (size() - 1) + ">");
            }

            return new ArrayList<>(list.subList(start, end));
        }

        @Override
        public int size() {
            return (int) Math.ceil((double) list.size() / (double) chunkSize);
        }
    }





Function call : 
              List<List<String>> containerNumChunks = PartitionUtil.ofSize(list, 999)

详情:https://e.printstacktrace.blog/divide-a-list-to-lists-of-n-size-in-Java-8/

其他回答

您可以将Guava库添加到项目中并使用列表。划分方法,例如:

List<Integer> bigList = ...
List<List<Integer>> smallerLists = Lists.partition(bigList, 10);
private ArrayList<List<String>> chunkArrayList(ArrayList<String> arrayToChunk, int chunkSize) {
    ArrayList<List<String>> chunkList = new ArrayList<>();
    int guide = arrayToChunk.size();
    int index = 0;
    int tale = chunkSize;
    while (tale < arrayToChunk.size()){
            chunkList.add(arrayToChunk.subList(index, tale));
            guide = guide - chunkSize;
            index = index + chunkSize;
            tale = tale + chunkSize;
    }
    if (guide >0) {
       chunkList.add(arrayToChunk.subList(index, index + guide));
    }
    Log.i("Chunked Array: " , chunkList.toString());
    return chunkList;
}

例子

    ArrayList<String> test = new ArrayList<>();
    for (int i=1; i<=1000; i++){
        test.add(String.valueOf(i));
    }

    chunkArrayList(test,10);

输出

分块:[[1,2,3,4,5,6,7,8,9,10),(11、12、13、14、15、16、17、18、19、20],[21日,22日,23日,24日,25日,26日,27日,28日,29日,30日],[第三十一条、第三十二条、第三十三,34岁,35岁,36岁,37岁,38岁,39岁,40],[41、42、43、44、45、46岁,47岁,48岁,49岁,50],[51岁,52岁,53岁,54岁,55岁,56岁,57岁的58岁的59岁60],[61,62,63,64,65,66,67,68,69,70],[71,72,73,74,75,76,77,78,79,80],[81,82,83,84,85,86,87,88,89,90],[91,92,93,94,95,96,97,98,99,100 ], .........

你会在日志里看到的

Java8流,一个表达式,没有其他库:

List<String> input = ...
int partitionSize = ...

 Collection<List<String>> partitionedList = IntStream.range(0, input.size())
    .boxed()
        .collect(Collectors.groupingBy(partition -> (partition / partitionSize), Collectors.mapping(elementIndex -> input.get(elementIndex), Collectors.toList())))
            .values();

测试:

List<String> input = Arrays.asList("a", "b", "c", "d", "e", "f", "g", "h" ,"i");

partitionSize = 1 - > [[a], [b], [c], [d], [e], [f], [g], [h],[我]] partitionSize = 2 - > [[a, b], c, d, e, f, g, h,[我]] partitionSize = 3 - > [a, b, c, d, e, f, g, h,我]] partitionSize = 7 - > [[a, b, c, d, e, f, g], [h,我]] partitionSize = 100 -> [[a, b, c, d, e, f, g, h, i]]

你也可以使用FunctionalJava库- List有分区方法。这个库有自己的集合类型,你可以将它们来回转换为java集合。

import fj.data.List;

java.util.List<String> javaList = Arrays.asList("a", "b", "c", "d" );

List<String> fList = Java.<String>Collection_List().f(javaList);

List<List<String> partitions = fList.partition(2);

如果你不想导入apache Commons库,试试下面这段简单的代码:

final static int MAX_ELEMENT = 20;

public static void main(final String[] args) {

    final List<String> list = new ArrayList<String>();

    for (int i = 1; i <= 161; i++) {
        list.add(String.valueOf(i));
        System.out.print("," + String.valueOf(i));
    }
    System.out.println("");
    System.out.println("### >>> ");
    final List<List<String>> result = splitList(list, MAX_ELEMENT);

    for (final List<String> entry : result) {
        System.out.println("------------------------");
        for (final String elm : entry) {
            System.out.println(elm);
        }
        System.out.println("------------------------");
    }

}

private static List<List<String>> splitList(final List<String> list, final int maxElement) {

    final List<List<String>> result = new ArrayList<List<String>>();

    final int div = list.size() / maxElement;

    System.out.println(div);

    for (int i = 0; i <= div; i++) {

        final int startIndex = i * maxElement;

        if (startIndex >= list.size()) {
            return result;
        }

        final int endIndex = (i + 1) * maxElement;

        if (endIndex < list.size()) {
            result.add(list.subList(startIndex, endIndex));
        } else {
            result.add(list.subList(startIndex, list.size()));
        }

    }

    return result;
}