java Hashmap : Get the key with maximum number of values

Question

I am trying to get the key with maximum number of values (not max value). I ave tried a couple of thing like counting values iterating over each key. But they boil down to problem finding a key from value which is problematic when we have same values.

    // calculate the length
    for(String key : map.keySet())
    {

        len.add(map.get(key).size());

    }

    // sort the length
    Collections.sort(len, Collections.reverseOrder() );

What version of Java are you using? If it's Java 8, it's a lot easier. — Louis Wasserman
– Louis Wasserman, Commented Dec 4, 2015 at 22:11
Possible duplicate answer http://stackoverflow.com/questions/5911174/finding-key-associated-with-max-value-in-a-java-map — Abdelhak
– Abdelhak, Commented Dec 4, 2015 at 22:17
for Map, each key can map to at most one value. Number of values for all keys will be either 0 or 1. — Eldar Budagov
– Eldar Budagov, Commented Dec 4, 2015 at 22:23

Louis Wasserman · Accepted Answer · 2015-12-04 22:15:18Z

2

If you're using Java 8, this could just be

String maxKey = map.entrySet().stream()
  .max(Comparator.comparingInt(entry -> entry.getValue().size()))
  .get().getKey();

if not, I'd tend to write this as

String maxKey = Collections.max(map.entrySet(), 
   new Comparator<Map.Entry<String, List<Value>>>() {
      @Override public int compare(
          Map.Entry<String, List<Value>> e1, Map.Entry<String, List<Value>> e2) {
        return Integer.compare(e1.getValue().size(), e2.getValue().size());
      }
   }).getKey();

...or, you could just write

String maxKey = null;
int maxCount = 0;
for (Map.Entry<String, List<Value>> entry : map.entrySet()) {
  if (entry.getValue().size() > maxCount) {
    maxKey = entry.getKey();
    maxCount = entry.getValue().size();
  }
}
return maxKey;

answered Dec 4, 2015 at 22:15

Louis Wasserman

200k26 gold badges367 silver badges437 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Jan Dörrenhaus · Accepted Answer · 2015-12-04 22:14:27Z

1

String maxKey = null;
for (String key : map.keySet())
{
    if (maxKey == null || map.get(key).size() > map.get(maxKey).size())
    {
        maxKey = key;
    }
}

This would be my solution to the problem. After execution, maxKey is key with the most values.

answered Dec 4, 2015 at 22:14

Jan Dörrenhaus

6,7172 gold badges36 silver badges45 bronze badges

1 Comment

maddie Over a year ago

Thanks @Jan Works like a charm. I was over complicating it by using so many unnecessary data structures.

Collectives™ on Stack Overflow

java Hashmap : Get the key with maximum number of values

2 Answers 2

Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related