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;
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
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;
}
其他回答
Java 8
我们可以根据大小或条件拆分列表。
static Collection<List<Integer>> partitionIntegerListBasedOnSize(List<Integer> inputList, int size) {
return inputList.stream()
.collect(Collectors.groupingBy(s -> (s-1)/size))
.values();
}
static <T> Collection<List<T>> partitionBasedOnSize(List<T> inputList, int size) {
final AtomicInteger counter = new AtomicInteger(0);
return inputList.stream()
.collect(Collectors.groupingBy(s -> counter.getAndIncrement()/size))
.values();
}
static <T> Collection<List<T>> partitionBasedOnCondition(List<T> inputList, Predicate<T> condition) {
return inputList.stream().collect(Collectors.partitioningBy(s-> (condition.test(s)))).values();
}
然后我们可以把它们用作:
final List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9,10);
System.out.println(partitionIntegerListBasedOnSize(list, 4)); // [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10]]
System.out.println(partitionBasedOnSize(list, 4)); // [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10]]
System.out.println(partitionBasedOnSize(list, 3)); // [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]
System.out.println(partitionBasedOnCondition(list, i -> i<6)); // [[6, 7, 8, 9, 10], [1, 2, 3, 4, 5]]
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);
**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/
这里讨论了一个类似的问题,Java:将List拆分为两个子列表?
主要可以使用子列表。更多细节:subblist
返回该列表中frommindex(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。)返回的列表受此列表支持,因此返回列表中的更改将反映在此列表中,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…
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;
}