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

List<List<Integer>> allChunkLists = new ArrayList<List<Integer>>();
List<Integer> chunkList = null;
int fromIndex = 0;
int toIndex = CHUNK_SIZE;

while (fromIndex < origList.size()) {
   chunkList = origList.subList(fromIndex, (toIndex > origList.size() ? origList.size() : toIndex));
   allChunkLists.add(chunkList);
   fromIndex = toIndex;
   toIndex += CHUNK_SIZE;
}

没有库,只有Java的subList()。toIndex需要适当地有界,以避免在subList()中出现越界错误。

其他回答

让我们假设您想要将列表分割为多个块的类作为库类。

所以让我们说这个类被称为“shared”,in应该是final,以确保它不会被扩展。

   import java.util.ArrayList;
   import java.util.Arrays;
   import java.util.List;

public final class Shared {
List<Integer> input;
int portion;

public Shared(int portion, Integer... input) {
    this.setPortion(portion);
    this.setInput(input);
}

public List<List<Integer>> listToChunks() {
    List<List<Integer>> result = new ArrayList<List<Integer>>();
    int size = this.size();
    int startAt = 0;
    int endAt = this.portion;

    while (endAt <= size) {

        result.add(this.input.subList(startAt, endAt));
        startAt = endAt;
        endAt = (size - endAt < this.portion && size - endAt > 0) ? (this.size()) : (endAt + this.portion);
    }

    return result;
}

public int size() {
    return this.input.size();
}

public void setInput(Integer... input) {
    if (input != null && input.length > 0)
        this.input = Arrays.asList(input);
    else
        System.out.println("Error 001 : please enter a valid array of integers.");
}

public void setPortion(int portion) {
    if (portion > 0)
        this.portion = portion;
    else
        System.out.println("Error 002 : please enter a valid positive number.");
}
}

接下来,让我们尝试从另一个持有公共静态void main(String…args)

public class exercise {

public static void main(String[] args) {
    Integer[] numbers = {1, 2, 3, 4, 5, 6, 7};
    int portion = 2;
    Shared share = new Shared(portion, numbers);
    System.out.println(share.listToChunks());   
}
}

现在,如果输入一个整数数组[1,2,3,4,5,6,7],分区为2。 结果将是[[1,2],[3,4],[5,6],[7]]

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]]

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);

您需要知道您划分列表的块大小。假设您有一个包含108个条目的列表,您需要25个块大小。因此,你最终会得到5个列表:

4项各有25项; 有8个元素的。

代码:

public static void main(String[] args) {

        List<Integer> list = new ArrayList<Integer>();
        for (int i=0; i<108; i++){
            list.add(i);
        }
        int size= list.size();
        int j=0;
                List< List<Integer> > splittedList = new ArrayList<List<Integer>>()  ;
                List<Integer> tempList = new ArrayList<Integer>();
        for(j=0;j<size;j++){
            tempList.add(list.get(j));
        if((j+1)%25==0){
            // chunk of 25 created and clearing tempList
            splittedList.add(tempList);
            tempList = null;
            //intializing it again for new chunk 
            tempList = new ArrayList<Integer>();
        }
        }
        if(size%25!=0){
            //adding the remaining enteries 
            splittedList.add(tempList);
        }
        for (int k=0;k<splittedList.size(); k++){
            //(k+1) because we started from k=0
            System.out.println("Chunk number: "+(k+1)+" has elements = "+splittedList.get(k).size());
        }
    }

你可以使用subList(int fromIndex, int toIndex)来获取原始列表的一部分。

来自API:

返回该列表中指定的fromIndex(包含)和toIndex(不包含)之间部分的视图。(如果fromIndex和toIndex相等,返回的列表为空。)返回的列表由该列表支持,因此返回列表中的非结构性更改会反映在该列表中,反之亦然。返回的列表支持该列表支持的所有可选列表操作。

例子:

List<Integer> numbers = new ArrayList<Integer>(
    Arrays.asList(5,3,1,2,9,5,0,7)
);

List<Integer> head = numbers.subList(0, 4);
List<Integer> tail = numbers.subList(4, 8);
System.out.println(head); // prints "[5, 3, 1, 2]"
System.out.println(tail); // prints "[9, 5, 0, 7]"

Collections.sort(head);
System.out.println(numbers); // prints "[1, 2, 3, 5, 9, 5, 0, 7]"

tail.add(-1);
System.out.println(numbers); // prints "[1, 2, 3, 5, 9, 5, 0, 7, -1]"

如果您需要这些切碎的列表不是一个视图,那么只需从subblist创建一个新的List。下面是一个把这些东西放在一起的例子:

// chops a list into non-view sublists of length L
static <T> List<List<T>> chopped(List<T> list, final int L) {
    List<List<T>> parts = new ArrayList<List<T>>();
    final int N = list.size();
    for (int i = 0; i < N; i += L) {
        parts.add(new ArrayList<T>(
            list.subList(i, Math.min(N, i + L)))
        );
    }
    return parts;
}


List<Integer> numbers = Collections.unmodifiableList(
    Arrays.asList(5,3,1,2,9,5,0,7)
);
List<List<Integer>> parts = chopped(numbers, 3);
System.out.println(parts); // prints "[[5, 3, 1], [2, 9, 5], [0, 7]]"
parts.get(0).add(-1);
System.out.println(parts); // prints "[[5, 3, 1, -1], [2, 9, 5], [0, 7]]"
System.out.println(numbers); // prints "[5, 3, 1, 2, 9, 5, 0, 7]" (unmodified!)