How to sort a treemap based on its values?

Question

How can I sort a treemap using its values rather than the key?

Answer 1

Try this. This sorts TreeMap values in ascending order, assuming that is how you want the values to be sorted.

static  Map sortByValues(Map map) {
        List list = new ArrayList(map.entrySet());

        // copy Map to List to use Comparator
        Collections.sort(list, new Comparator() {
            public int compare(Object o1, Object o2) {
                return ((Comparable) ((Map.Entry) o1).getValue()).compareTo(((Map.Entry) o2).getValue());
            }
        });

        // then copy List to LinkedHashMap as it preserves insertion order
        Map result = new LinkedHashMap();
        Iterator itr = list.iterator();
        while (itr.hasNext()) {
            Map.Entry m = (Map.Entry) itr.next();
            result.put(m.getKey(), m.getValue());
        }

        return result;
    }