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up vote 1 down vote favorite

I have seen this question asked a few times, but I do not entirely understand the solutions provided. Below is a bit of code I came up with for splitting up an arraylist into five parts. I have tested and changed the array size from 0 to 16 and it works fine.

I am sure there is a "better" way of doing this, so I would like to see what others think.

public static void main(String[] args)
{
    ArrayList<String> arrayList = new ArrayList<String>();
    arrayList.add("A");//1
    arrayList.add("B");//2
    arrayList.add("C");//3
    arrayList.add("D");//4
    arrayList.add("E");//5
    arrayList.add("F");//6
    arrayList.add("G");//7
    arrayList.add("H");//8
    arrayList.add("I");//9
    arrayList.add("J");//10
    arrayList.add("K");//11
    arrayList.add("L");//12
    arrayList.add("M");//13
    arrayList.add("N");//14
    arrayList.add("O");//15
    arrayList.add("P");//16
    arrayList.add("X");//17

    int i1 = (int) Math.ceil(arrayList.size()/5.0);

    List<String> sublist = new ArrayList<String>();
    int x=0;
    for(int p=0; p<i1; p++)
    {
        if(arrayList.size()>=(x+5))
        {
            sublist = new ArrayList<String>(arrayList.subList(x, x+5));
            x+=5;
        }
        else
            sublist = new ArrayList<String>(arrayList.subList(x, arrayList.size()));
        for(String slist : sublist)
        {
            System.out.println("i:"+slist);
        }
    }
}
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migrated from stackoverflow.com Jun 28 '13 at 20:58

This question came from our site for professional and enthusiast programmers.

1 Answer 1

up vote 2 down vote

How about this:

public static void main(String[] args) {
    List<String> arrayList = new ArrayList<String>();
    for (int i = 0; i < 23; i++) {
        arrayList.add(String.valueOf(i));
    }

    for (int start = 0; start < arrayList.size(); start += 5) {
        int end = Math.min(start + 5, arrayList.size());
        List<String> sublist = arrayList.subList(start, end);
        System.out.println(sublist);
    }
}

So instead of counting the segment of the list and increasing a second counter by 5 each time, you can just increase the first counter by five in the third argument of the for loop. Also, you can use the result of subList directly, without passing it to a constructor first. And you can get rid of the if-else by using min to determine the end index.

Output:

[0, 1, 2, 3, 4]
[5, 6, 7, 8, 9]
[10, 11, 12, 13, 14]
[15, 16, 17, 18, 19]
[20, 21, 22]
share|improve this answer
    
How to split array list in to equal parts of we dont know the chunk size (5 in your case) but we know the number of parts we want to make. e.g. how to split above 23 items in to 4 parts (dont know how many items should go to each part). My real use case is to split big file in to number of files –  user1191081 Jun 13 at 11:51
    
@user1191081 Maybe I'm missing something, but you just divide? 23 items to 4 parts -> 23/4 == 5.something -> 6 parts, i.e. ceil(numItems/numParts). –  tobias_k Jun 13 at 11:53

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