Sort a set containing list

Question

I have many lists, every list contains 4 elements all string. Now I have a Set<List> which stores all the above lists.

I want to sort the set on the basis of a field in list.

eg. list1=["x","2"], list2=["a","5"], list3=["g","1"] and set.add(list1), set.add(list2), set.add(list3).

Now I want to sort that set on the basis of 2nd fields in list.

You can use a TreeSet, as shown here http://stackoverflow.com/questions/4165832/sorting-values-of-set. — Mario Ishac, Dec 23 '15 at 07:01
You can use `Collections.sort()` method by implementing the `Comparator` interface for additional parameter. — Hemang, Dec 23 '15 at 07:03
there is difference between that scenerio and mine. Treeset dont work in mine scenerio. — Piyush Singh, Dec 23 '15 at 07:03
Then use comparator or comparable interfaces to implement your scenarios — Rajnikant Patel, Dec 23 '15 at 07:13

score 1 · Accepted Answer · answered Dec 23 '15 at 07:19

So you have like this:

 List<String> list1 = Arrays.asList("x", "2");
 List<String> list2 = Arrays.asList("a", "5");
 List<String> list3 = Arrays.asList("g", "1");

And one super-list

 Set<List<String>> set = new HashSet<List<String>>();
 set.add(list1);
 set.add(list2);
 set.add(list3);

And you need a sorted List over the second String:

    List<List<String>> list = new ArrayList<List<String>>(set);
    Collections.sort(list, new Comparator<List<String>>() {

        @Override
        public int compare(List<String> o1, List<String> o2) {
            //Index 1 = second element
            return o1.get(1).compareTo(o2.get(1));
        }

     });

Full Example

List list1 = Arrays.asList("x", "2"); List list2 = Arrays.asList("a", "5"); List list3 = Arrays.asList("g", "1");

     Set<List<String>> set = new HashSet<List<String>>();
     set.add(list1);
     set.add(list2);
     set.add(list3);

     List<List<String>> list = new ArrayList<List<String>>(set);
     Collections.sort(list, new Comparator<List<String>>() {

        @Override
        public int compare(List<String> o1, List<String> o2) {
            //Index 1 = second element
            return o1.get(1).compareTo(o2.get(1));
        }

     });
     for(List<String> li : list) {
         System.out.println(li);
     }

Creates this output / sorting:

[g, 1]
[x, 2]
[a, 5]

@SergiyMedvynskyy it's just the assumption that the Set is already in place - the comments to the question mentioned TreeSet "would not work" — Jan, Dec 23 '15 at 07:34

Sort a set containing list

1 Answers1