How to split ArrayList into another List

Question

I'm trying to split an ArrayList into separate blocks. I have a function that returns table data collected in jsoupie, just as individual elements. I wonder how to make a second list, so that it consisted of every 5 subsequent elements of the first list.

   example:
    1 list:
    lista1.get (0) = Monday;
    lista1.get (1) = Tuesday;
    ...
    lista1.get (6) = Sunday;

    and here I would like to make it

                     //lista1.get(1) .. lista1.get(6)
    lista2.get (0) = Monday, Tuesday, Wednesday, Thursday, Friday;
    lista2.get (1) = any, other data contained in, this, leaves, stated below;

Thanks

Are you going to create a list of list? use subList on the first list and add to a new list — dragon66
– dragon66, Commented Sep 23, 2014 at 16:35
From you Question it's look like you should try list of list. — Janny
– Janny, Commented Sep 23, 2014 at 16:36
Yes, I would like to create list of every 5 elements head lists, but I get data from JSOUP table (website) , and I don't know how many datas is there, so I want to split this array by every 5 subsequent — Algeroth
– Algeroth, Commented Sep 23, 2014 at 16:40

Aivean · Accepted Answer · 2014-09-23 16:43:27Z

I have written two methods for you. One splits your list into list of lists, another one groups nested lists into single string.

    public class LinkedListSplitByFive {

        private static List<List<String>> splitByGroupAsList(List<String> list, int elementsInGroup) {
            List<List<String>> result = new ArrayList<List<String>>();

            List<String> group = new ArrayList<String>(elementsInGroup);
            for (String s : list) {
                group.add(s);
                if (group.size() == elementsInGroup) {
                    result.add(group);
                    group = new ArrayList<String>(elementsInGroup);
                }
            }
            if (!group.isEmpty()) {
                result.add(group);
            }
            return result;
        }

        private static List<String> splitByGroupAsString(List<String> list, int elementsInGroup) {
            List<List<String>> lists = splitByGroupAsList(list, elementsInGroup);
            List<String> result = new ArrayList<String>(lists.size());

            for (List<String> group : lists) {
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < group.size(); i++) {
                    sb.append(group.get(i));
                    if (i == group.size() - 1) {
                        sb.append(";");
                    } else {
                        sb.append(", ");
                    }
                }
                result.add(sb.toString());
            }
            return result;
        }

        public static void main(String[] args) {

            List<String> list = Arrays.asList("1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11");

            System.out.println(splitByGroupAsList(list, 5));
            // [[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11]]

            System.out.println(splitByGroupAsString(list, 5));
            // [1, 2, 3, 4, 5;, 6, 7, 8, 9, 10;, 11;]
        }
    }

przemek hertel · Accepted Answer · 2014-09-23 16:40:09Z

1

Try something like this:

public static void main(String[] args) {

    List<String> flatList = Arrays.asList(
          "1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11");

    List<List<String>> outer = new ArrayList<List<String>>();

    int cnt = 0;
    List<String> inner = new ArrayList<String>(5);

    for (String str : flatList) {
        inner.add(str);    // fill inner list

        if (++cnt == 5) {
            outer.add(inner);
            inner = new ArrayList<String>(5);
            cnt = 0;
        }
    }

    if (!inner.isEmpty()) {
        outer.add(inner);
    }

    System.out.println(outer);
}

Result of this code is:

[[1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11]]

answered Sep 23, 2014 at 16:40

przemek hertel

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2 Comments

Algeroth Over a year ago

But, can you explain me, what should I do when I want to return List<String>? Because now, I'm getting a List<List<String>

Aivean Over a year ago

@Algeroth check my answer below. It answers this question too.

Luciana Campello · Accepted Answer · 2014-09-23 16:40:21Z

0

You can also try a map of Object* with List.
* Change Object for whatever you need.

answered Sep 23, 2014 at 16:40

Luciana Campello

1014 bronze badges

Comments

santosh-patil · Accepted Answer · 2014-09-23 17:11:00Z

0

Considering you need a list of lists as output, you can try this. I haven't tried compiling it, so there might be some syntax errors and typos. But the main idea is to keep picking 5 elements each time from the original list and adding those into new list. And keeping a listOfLists, which eventually contains all such new lists.

ArrayList<ArrayList<String>> listOfLists = new ArrayList<ArrayList<String>>();
    int size=list.length %5=0?i/5:i/5+1;
    for(int i=0;i<size;i++){
        listOfLists.add(Arrays.copyOfRange(list, i*5, i*5+5));
    }
# return listOfLists;

edited Sep 23, 2014 at 17:11

answered Sep 23, 2014 at 16:47

santosh-patil

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2 Comments

Aivean Over a year ago

Considering you are using list.size(), list is the subclass of Collection. Then how can you pass it as argument to Arrays.copyOfRange which accepts only plain arrays?

santosh-patil Over a year ago

I considered input list as an array. I should have used length attribute instead of size(), thanks for pointing it out. Even if the input is ArrayList, one can convert it into an array before passing it to Arrays.copyOfRange() method. Of corse, it might not be the most efficient way.

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