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
**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
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。
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);
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
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;
}
}
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。