CODEWITHSUNDEEP
javasortingdictionary
ealeon
ealeon

Reputation: 12452

Best way to sort Map with Values

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

Upvotes: 4

Views: 2069

Answers (2)

amit
amit

Reputation: 178451

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

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

Upvotes: 2

Amir Pashazadeh
Amir Pashazadeh

Reputation: 7302

Use Google Guava. It contains BiMap implementations which can be inversed, and then just sort on inversed map keys.

Map<Character, Integer> myMap = HashBiMap.create();
// put your values in myMap
Map<Integer, Character> inversed = myMap.inverse();
SortedMap<Integer, Character> sortedInversed = new TreeMap<Integer, Character>(inversed);

so just iterate the sortedInversed

Upvotes: 1

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