How to implement sorted set in descending order?

Question

I have key, value pairs. The key is a String and the values are integers. I would want to sort it in descending order so that the element with the highest value appears first.

How do I sort a sorted set in descending order ?

i tried treemap but i wasnot arranging it in descending order — kritika goyal, Aug 21 '15 at 11:37
See http://stackoverflow.com/questions/22212412/sort-a-set-in-reverse-order — Raedwald, Aug 21 '15 at 11:39
Possible duplicate http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java — user3589553, Aug 21 '15 at 11:39
possible duplicate of [How do I reverse the order of the data in a TreeSet instance?](http://stackoverflow.com/questions/12960970/how-do-i-reverse-the-order-of-the-data-in-a-treeset-instance) — Raedwald, Aug 21 '15 at 11:40
if you have a TreeMap, then it has a descendingMap() method, which return desc sorted collection of elements — Stanislav, Aug 21 '15 at 11:43

Stanislav · Answer 1 · 2015-08-21T12:19:43.573

1

You can do it with TreeMap, for example:

//any not sorted map
Map<String, Integer> map = new HashMap<>();
map.put("567", 567);
map.put("456", 456);
map.put("123", 123);

//create sorted TreeMap with descending sorting
Map<String, Integer> sortedMap = new TreeMap<String, Integer>(Collections.reverseOrder());
sorted.putAll(map);

If you wish to sort it by values, then you can make it so:

private static Map<String, Integer> sortByComparator(Map<String, Integer> unsortedMap) {

    List<Map.Entry<String, Integer>> list = new LinkedList<Map.Entry<String, Integer>>(unsortedMap.entrySet());

    Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
        public int compare(Map.Entry<String, Integer> o1,
                           Map.Entry<String, Integer> o2) {
            return (o2.getValue()).compareTo(o1.getValue());
        }
    });

    Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
    for (Iterator<Map.Entry<String, Integer>> it = list.iterator(); it.hasNext();) {
        Map.Entry<String, Integer> entry = it.next();
        sortedMap.put(entry.getKey(), entry.getValue());
    }
    return sortedMap;
}

edited Aug 21 '15 at 12:19

answered Aug 21 '15 at 11:39

Stanislav

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I am using collection first time? – kritika goyal Aug 21 '15 at 11:45
itarat over it via it's entries: for (Map.Entry entry : sortedMap.entrySet()) { System.out.println(entry.getKey() + "/" + entry.getValue()); } – Stanislav Aug 21 '15 at 11:49
iterating or sorting? – Stanislav Aug 21 '15 at 11:52
So, then I need to see your code, to tell, what is wrong – Stanislav Aug 21 '15 at 11:56
hey is it sort the map by key only? – kritika goyal Aug 21 '15 at 11:57
Yes, just by it's key – Stanislav Aug 21 '15 at 12:00
is there anyway to sort it by value – kritika goyal Aug 21 '15 at 12:01
ok thanks , I make some changes like I exchange the key and value pairs but now another issue all the elements are not adding into it only first element is added in map – kritika goyal Aug 21 '15 at 12:18
changed the answer, added sorting by value – Stanislav Aug 21 '15 at 12:19

How to implement sorted set in descending order?

1 Answers1