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

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);

其他回答

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;
}

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!)

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());
        }
    }

只是要明确一点,这还需要更多的测试…

public class Splitter {

public static <T> List<List<T>> splitList(List<T> listTobeSplit, int size) {
    List<List<T>> sublists= new LinkedList<>();
    if(listTobeSplit.size()>size) {
    int counter=0;
    boolean lastListadded=false;

    List<T> subList=new LinkedList<>();

    for(T t: listTobeSplit) {           
         if (counter==0) {               
             subList =new LinkedList<>();
             subList.add(t);
             counter++;
             lastListadded=false;
         }
         else if(counter>0 && counter<size-1) {
             subList.add(t);
             counter++;
         }
         else {
             lastListadded=true;
             subList.add(t);
             sublists.add(subList);
             counter=0;
         }              
    }
    if(lastListadded==false)
        sublists.add(subList);      
    }
    else {
        sublists.add(listTobeSplit);
    }
    log.debug("sublists: "+sublists);
    return sublists;
 }
}
import org.apache.commons.collections4.ListUtils;
ArrayList<Integer> mainList = .............;
List<List<Integer>> multipleLists = ListUtils.partition(mainList,100);
int i=1;
for (List<Integer> indexedList : multipleLists){
  System.out.println("Values in List "+i);
  for (Integer value : indexedList)
    System.out.println(value);
i++;
}