Sorting of arraylist of multiple arraylists

Question

I have an arraylist of multiple arraylists like-

ArrayList<ArrayList<String>> al1=new ArrayList<ArrayList<String>>();

the arraylist contains the elements:

[[Total for all Journals, IOP, IOPscience, , , , , 86, 16, 70, 17, 8, 14, 6, 17, 19, 5], [2D Materials, IOP, IOPscience, 10.1088/issn.2053-1583, 2053-1583, , 2053-1583, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [Acta Physica Sinica (Overseas Edition), IOP, IOPscience, 10.1088/issn.1004-423X, 1004-423X, 1004-423X, , 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [Advances in Natural Sciences: Nanoscience and Nanotechnology, IOP, IOPscience, 10.1088/issn.2043-6262, 2043-6262, , 2043-6262, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], [Applied Physics Express, IOP, IOPscience, , 1882-0786, 1882-0778, 1882-0786, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]]

Now i want to sort the main arraylist. Main arraylist contains 5 inner arraylists.Now the sorting must be like the 7th element of every inner arraylist is compared which is integer and inner arraylists are arranged accorting to the value of their 7th element.

Collections.sort(al1, new Comparator<ArrayList<String>>() {
  @Override public int compare(ArrayList<String> o1, ArrayList<String> o2) {
    return o1.get(7).compareTo(o2.get(7));
  }
});

I am trying to make own comparator but everytime i got wrong result. — monu dwivedi
– monu dwivedi, Commented Nov 20, 2014 at 9:03
Show us your code. Describe what you think it does. Show us the intended output. Show us the actual output of your code. — user1907906
– user1907906, Commented Nov 20, 2014 at 9:04
Sounds like you should use a class rather than a List with elements that have special significance at specific indexes. — Bohemian
– Bohemian ♦, Commented Nov 20, 2014 at 9:11

ToYonos · Accepted Answer · 2014-11-20 09:15:28Z

1

Indexes in Java begin at 0. The 7th element has the index 6. Moreover, you have to convert the String to int in order to be properly compared.

Try this :

Comparator<ArrayList<String>> cmp = new Comparator<ArrayList<String>>()
{
    public int compare(ArrayList<String> a1, ArrayList<String> a2)
    {
        // TODO check for null value
        return new Integer(a1.get(6)).compareTo(new Integer(a2.get(6));
    }
};

Collections.sort(yourList, cmp);

edited Nov 20, 2014 at 9:15

answered Nov 20, 2014 at 9:06

ToYonos

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3 Comments

ToYonos Over a year ago

I made a modification

Dmitry Ginzburg Over a year ago

Integer.parseInt is always better, than new Integer

ToYonos Over a year ago

Yes, but i wanted to keep an object to use compareTo

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