Sort List of List

Question

I have List of Lists(list rows contain list column). I want to sort my rows in ListRZS by length(.size()).

[[123, 189, 277], [11], [145, 211, 299], [156, 222, 310], [167, 233, 255], [189, 266], [200, 277], [211, 288], [245, 299], [233], [244]]

Shoul be:
[[11], [233], [244], [189, 266],[200, 277], [211, 288], [245, 299], [123, 189, 277], [145, 211, 299], [156, 222, 310], [167, 233, 255]]

Question: How to write working comporator/comparable for this situation.

public class Start {
public static void main(String[] args) {
    System.out.println("Start reading from Xls");
    ReaderXls1Column read = new ReaderXls1Column();
    ReaderXls readrzs = new ReaderXls();
    List<String> listASU = new ArrayList<String>(read.ReaderXls1Column("Text1obj",0,1));                        // Creating Lists
    List<List<String>>  listRZS = new ArrayList<List<String>>(readrzs.ReadXls("Text1obj",2,12));
    System.out.println(listASU);
    System.out.println(listRZS);
    System.out.println("Reading is over");
    System.out.println(listRZS);
    WriterXls.main("Text1obj",listRZS);
    System.out.println("Writing is over");
}

My attempt without comparator, comparable(of course, not working right)

        int k=0;
    while ( k<listRZS.size()){
        for (int j=0;j<10;j++)     {
            List<String> tmplist = new ArrayList<String>();
            if (listRZS.get(k).size()>listRZS.get(k+1).size()) {Collections.copy(listRZS.get(k),tmplist); listRZS.remove(k); listRZS.add(k+1,tmplist);}
            else {};
        }
        Collections.sort(listRZS.get(k));       // sort each row, solution above
        k++;
    }

score 2 · Accepted Answer · edited May 23 '17 at 10:31

A comparator just needs to implement one method (compare), that takes two items, and returns:

0 if they are equal
positive value if the second is less than the first
negative value if the second is greater than the first.

When sorting integer values, a typical pattern to accomplish this is to reduce each object received in the compare method to an integer, then, if we call them a and b, simply return a - b.

Example (see it running at ideone.com/rcmDbi):

import java.util.*;

class Test {

    public static void main(String[] args) {
        List<Integer> a = Arrays.asList(1);
        List<Integer> b = Arrays.asList(1,2);
        List<Integer> c = Arrays.asList(1,2,3);
        List<Integer> d = Arrays.asList(1,2,3,4);

        List<List<Integer>> test = Arrays.asList(d,b,c,a);
        Collections.sort(test, ListSizeComparator.INSTANCE);
        for (List<Integer> list : test) {
            System.out.println(list.size());
        }
    }

    enum ListSizeComparator implements Comparator<List> {
        INSTANCE;

        public int compare(List one, List other) {
            return one.size() - other.size();
        }
    }
}

(By the way, I've used an enum for the enum singleton pattern because our Comparator stores no state.)

@Eldar This comparator will work for any type of list. In fact, you could change it to Collection and it would work for any Collection. Notice how it doesn't do anything with the contents. — Nicole, Aug 13 '13 at 06:09

score 1 · Answer 2 · answered Aug 13 '13 at 05:35

1

Try like this:

List<List<String>>  myList; // load myList with values

Then do the sorting as follows:

 Collections.sort(myList, new Comparator<List<String>>(){

    @Override
    public int compare(List<String> arg0, List<String> arg1) {

        return arg1.size() - arg0.size();
    }

    });

answered Aug 13 '13 at 05:35

Suji

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result: [189, 266, 277] result is completely different; – Eldar Aug 13 '13 at 05:51
what you mean by 'result is completely different'? whats the issue? – Suji Aug 13 '13 at 06:39

Sort List of List

2 Answers2