How to split array list into equal parts?

Question

Is there anyway to split ArrayList into different parts without knowing size of it until runtime? I know there is a method called:

list.subList(a,b);
         


        

Answer 1

listSize = oldlist.size();
chunksize =1000;
chunks = list.size()/chunksize;
ArrayList subLists;
ArrayList finalList;
int count = -1;
for(int i=0;i<chunks;i++){
     subLists = new ArrayList();
     int j=0;
     while(j<chunksize && count<listSize){
        subList.add(oldList.get(++count))
        j++;
     }
     finalList.add(subLists)
}

You can use this finalList as it contains the list of chuncks of the oldList.

Answer 2

If you're constrained by PL/SQL in limits then you want to know how to split a list into chunks of size <=n, where n is the limit. This is a much simpler problem as it does not require knowing the size of the list in advance.

Pseudocode:

for (int n=0; n<list.size(); n+=limit)
{
    chunkSize = min(list.size,n+limit);
    chunk     = list.sublist(n,chunkSize);
    // do something with chunk
}

Answer 3

generic method for your help :

private static List<List<Object>> createBatch(List<Object> originalList,
        int chunkSize) {
    List<List<Object>> listOfChunks = new ArrayList<List<Object>>();
    for (int i = 0; i < originalList.size() / chunkSize; i++) {
        listOfChunks.add(originalList.subList(i * chunkSize, i * chunkSize
                + chunkSize));
    }
    if (originalList.size() % chunkSize != 0) {
        listOfChunks.add(originalList.subList(originalList.size()
                - originalList.size() % chunkSize, originalList.size()));
    }
    return listOfChunks;