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
你可以使用Eclipse Collections中的chunk方法:
ArrayList<Integer> list = new ArrayList<>(Interval.oneTo(1000));
RichIterable<RichIterable<Integer>> chunks = Iterate.chunk(list, 10);
Verify.assertSize(100, chunks);
这篇DZone文章中还包含了一些块方法的示例。
注意:我是Eclipse Collections的提交者。
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]]
我猜你遇到的问题是命名100个数组列表并填充它们。您可以创建一个数组列表数组,并使用循环填充每个数组列表。
最简单(也是最愚蠢的)的方法是这样的:
ArrayList results = new ArrayList(1000);
// populate results here
for (int i = 0; i < 1000; i++) {
results.add(i);
}
ArrayList[] resultGroups = new ArrayList[100];
// initialize all your small ArrayList groups
for (int i = 0; i < 100; i++) {
resultGroups[i] = new ArrayList();
}
// put your results into those arrays
for (int i = 0; i < 1000; i++) {
resultGroups[i/10].add(results.get(i));
}
创建一个新列表,并使用addAll()方法添加源列表的子列表视图以创建新的子列表
List<T> newList = new ArrayList<T>();
newList.addAll(sourceList.subList(startIndex, endIndex));
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]]
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;
}
}