Question

private Map<Character, Integer> frequencies;

I have a Map with Character being Key and its associated Integer being Value.

Whats the best/fastest/efficeint way to sort by Value?

i.e Map may have
a,1
c,10
p,5
s,7
and after sorted,
it would be
a,1
p,5
s,7
c,10

I was thinking about doing it with Priority Queue and with integer but i would lose the Character value if the integer vals are duplicates

Answer 1

A priority queue is a decent approach – all you need to do is get the Entry set from the map, and override a Comparator as the input to the queue.

Map<Character,Integer> map = new HashMap<Character, Integer>();
map.put('a',1);
map.put('c',10);
map.put('p',5);
map.put('2',7);
PriorityQueue<Entry<Character, Integer>> pq = new PriorityQueue<Map.Entry<Character,Integer>>(map.size(), new Comparator<Entry<Character, Integer>>() {

    @Override
    public int compare(Entry<Character, Integer> arg0,
            Entry<Character, Integer> arg1) {
        return arg0.getValue().compareTo(arg1.getValue());
    }
});
pq.addAll(map.entrySet());
while (!pq.isEmpty()) {
    System.out.println(pq.poll());
}

Will yield (as expected):

a=1
p=5
2=7
c=10

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Note: Avoid using a Set or a Map with keys as the values of the map – because it will NOT handle duplicate values well.