Key for maximum value in Hashtable

Question

Hi I have the following object:

Hashtable<Object, Double>

and I want to find the key of the maximum Double value in the table. Easiest way to do that?

Thanks

Solution 1

There is no built in function to get the maximum value out of a Hashtable you are going to have to loop over all the keys and manually determine the max.

Object maxKey=null;
Double maxValue = Double.MIN_VALUE; 
for(Map.Entry<Object,Double> entry : table.entrySet()) {
     if(entry.getValue() > maxValue) {
         maxValue = entry.getValue();
         maxKey = entry.getKey();
     }
}

Edit: To find more than 1 key for the max value

ArrayList<Object> maxKeys= new ArrayList<Object>();
Double maxValue = Double.MIN_VALUE; 
for(Map.Entry<Object,Double> entry : table.entrySet()) {
     if(entry.getValue() > maxValue) {
         maxKeys.clear(); /* New max remove all current keys */
         maxKeys.add(entry.getKey());
         maxValue = entry.getValue();
     }
     else if(entry.getValue() == maxValue)
     {
       maxKeys.add(entry.getKey());
     }
}

Solution 2

If it's really important you do it without iterating all keys, simply extend HashTable

class MyHashtable extends Hashtable<Object, Double> {

    private Double maxValue = Double.MIN_VALUE;

    @Override
    public synchronized Double put(Object k, Double v) {
        maxValue = Math.max(maxValue, v);
        return super.put(k, v);
    }

    @Override
    public synchronized void clear() {
        super.clear();
        maxValue = Double.MIN_VALUE;
    }

    public Double getMaxValue() {
        return maxValue;
    }

    @Override
    public synchronized Double remove(Object key) {
        // TODO: Left as an Excercise for the user, refer the other answers
        return super.remove(key);
    }
}

Comments

[Learner]

Can I know, what happens if their are two highest values?

[Learner]

what I am suppose to do to find both values key

[Learner]

Can I know, what happens if their are two highest values? what I am suppose to do to find both values key? thx in advance

[twain249]

@Learner check the edit to handle multiple keys with the same max value

[twain249]

This finds all the keys that replace the old maximum value. With your test set it should have returned 'c' and 'd' not 'b' and 'd'.

[AnV]

your algorithm/code gives the wrong answer. As @twain249 said, it finds all keys that replace old max value. It should rather find a key which has max value or all the keys which have their value as max value.