Finding Key associated with max Value in a Java Map

What is the easiest way to get key ass开发者_如何学JAVAociated with the max value in a map?

I believe that Collections.max(someMap) will return the max Key, when you want the key that corresponds to the max value.

For completeness, here is a java-8 way of doing it

countMap.entrySet().stream().max((entry1, entry2) -> entry1.getValue() > entry2.getValue() ? 1 : -1).get().getKey();

or

Collections.max(countMap.entrySet(), (entry1, entry2) -> entry1.getValue() - entry2.getValue()).getKey();

or

Collections.max(countMap.entrySet(), Comparator.comparingInt(Map.Entry::getValue)).getKey();

Basically you'd need to iterate over the map's entry set, remembering both the "currently known maximum" and the key associated with it. (Or just the entry containing both, of course.)

For example:

Map.Entry<Foo, Bar> maxEntry = null;

for (Map.Entry<Foo, Bar> entry : map.entrySet())
{
    if (maxEntry == null || entry.getValue().compareTo(maxEntry.getValue()) > 0)
    {
        maxEntry = entry;
    }
}

A simple one liner using Java-8

Key key = Collections.max(map.entrySet(), Map.Entry.comparingByValue()).getKey();

This code will print all the keys with maximum value

public class NewClass4 {
    public static void main(String[] args)
    {
        HashMap<Integer,Integer>map=new HashMap<Integer, Integer>();
        map.put(1, 50);
        map.put(2, 60);
        map.put(3, 30);
        map.put(4, 60);
        map.put(5, 60);
        int maxValueInMap=(Collections.max(map.values()));  // This will return max value in the HashMap
        for (Entry<Integer, Integer> entry : map.entrySet()) {  // Iterate through HashMap
            if (entry.getValue()==maxValueInMap) {
                System.out.println(entry.getKey());     // Print the key with max value
            }
        }

    }
}

Here's how do do it directly (without an explicit extra loop) by defining the appropriate Comparator:

int keyOfMaxValue = Collections.max(
                        yourMap.entrySet(), 
                        new Comparator<Entry<Double,Integer>>(){
                            @Override
                            public int compare(Entry<Integer, Integer> o1, Entry<Integer, Integer> o2) {
                                return o1.getValue() > o2.getValue()? 1:-1;
                            }
                        }).getKey();

1. Using Stream

public <K, V extends Comparable<V>> V maxUsingStreamAndLambda(Map<K, V> map) {
    Optional<Entry<K, V>> maxEntry = map.entrySet()
        .stream()
        .max((Entry<K, V> e1, Entry<K, V> e2) -> e1.getValue()
            .compareTo(e2.getValue())
        );
     
    return maxEntry.get().getKey();
}

2. Using Collections.max() with a Lambda Expression

    public <K, V extends Comparable<V>> V maxUsingCollectionsMaxAndLambda(Map<K, V> map) {
        Entry<K, V> maxEntry = Collections.max(map.entrySet(), (Entry<K, V> e1, Entry<K, V> e2) -> e1.getValue()
            .compareTo(e2.getValue()));
        return maxEntry.getKey();
    }

3. Using Stream with Method Reference

    public <K, V extends Comparable<V>> V maxUsingStreamAndMethodReference(Map<K, V> map) {
        Optional<Entry<K, V>> maxEntry = map.entrySet()
            .stream()
            .max(Map.Entry.comparingByValue());
        return maxEntry.get()
            .getKey();
    }

4. Using Collections.max()

    public <K, V extends Comparable<V>> V maxUsingCollectionsMax(Map<K, V> map) {
        Entry<K, V> maxEntry = Collections.max(map.entrySet(), new Comparator<Entry<K, V>>() {
            public int compare(Entry<K, V> e1, Entry<K, V> e2) {
                return e1.getValue()
                    .compareTo(e2.getValue());
            }
        });
        return maxEntry.getKey();
    }

5. Using Simple Iteration

public <K, V extends Comparable<V>> V maxUsingIteration(Map<K, V> map) {
    Map.Entry<K, V> maxEntry = null;
    for (Map.Entry<K, V> entry : map.entrySet()) {
        if (maxEntry == null || entry.getValue()
            .compareTo(maxEntry.getValue()) > 0) {
            maxEntry = entry;
        }
    }
    return maxEntry.getKey();
}

An answer that returns an Optional since the map may have no max value if it is empty: map.entrySet().stream().max(Map.Entry.comparingByValue()).map(Map.Entry::getKey);

I have two methods, using this méthod to get the key with the max value:

 public static Entry<String, Integer> getMaxEntry(Map<String, Integer> map){        
    Entry<String, Integer> maxEntry = null;
    Integer max = Collections.max(map.values());

    for(Entry<String, Integer> entry : map.entrySet()) {
        Integer value = entry.getValue();
        if(null != value && max == value) {
            maxEntry = entry;
        }
    }
    return maxEntry;
}

As an example gettin the Entry with the max value using the method:

  Map.Entry<String, Integer> maxEntry =  getMaxEntry(map);

Using Java 8 we can get an object containing the max value:

Object maxEntry = Collections.max(map.entrySet(), Map.Entry.comparingByValue()).getKey();      

System.out.println("maxEntry = " + maxEntry);

Simple to understand. In Below code, maxKey is the key which is holding the max value.

int maxKey = 0;
int maxValue = 0;
for(int i : birds.keySet())
{
    if(birds.get(i) > maxValue)
    {
        maxKey = i;
        maxValue = birds.get(i);
    }
}

Java 8 way to get all keys with max value.

Integer max = PROVIDED_MAP.entrySet()
            .stream()
            .max((entry1, entry2) -> entry1.getValue() > entry2.getValue() ? 1 : -1)
            .get()
            .getValue();

List listOfMax = PROVIDED_MAP.entrySet()
            .stream()
            .filter(entry -> entry.getValue() == max)
            .map(Map.Entry::getKey)
            .collect(Collectors.toList());

System.out.println(listOfMax);

Also you can parallelize it by using parallelStream() instead of stream()

given map

HashMap abc = new HashMap<>();

get all map entries with a maximum of values.

you can use any of the below methods in the filter to get respective map entries for sets of minimum or maximum values

Collections.max(abc.values())
Collections.min(abc.values())
Collections.max(abc.keys())
Collections.max(abc.keys())

abc.entrySet().stream().filter(entry -> entry.getValue() == Collections.max(abc.values()))

if only want to get the keys for the filter map

abc.entrySet()
       .stream()
       .filter(entry -> entry.getValue() == Collections.max(abc.values()))
       .map(Map.Entry::getKey);

if you want to get the values for the filtered map

abc.entrySet()
      .stream()
      .filter(entry -> entry.getValue() == Collections.max(abc.values()))
      .map(Map.Entry::getvalue)

if you want to get all such keys in a list:

abc.entrySet()
  .stream()
  .filter(entry -> entry.getValue() == Collections.max(abc.values()))
  .map(Map.Entry::getKey)
  .collect(Collectors.toList())

if you want to get all such values in a list:

abc.entrySet()
  .stream()
  .filter(entry -> entry.getValue() == Collections.max(abc.values()))
  .map(Map.Entry::getvalue)
  .collect(Collectors.toList())

Is this solution ok?

int[] a = { 1, 2, 3, 4, 5, 6, 7, 7, 7, 7 };
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
for (int i : a) {
Integer count = map.get(i);
map.put(i, count != null ? count + 1 : 0);
}
Integer max = Collections.max(map.keySet());
System.out.println(max);
System.out.println(map);

int maxValue = 0;
int mKey = 0;
for(Integer key: map.keySet()){
    if(map.get(key) > maxValue){
        maxValue = map.get(key);
        mKey = key;
    }
}
System.out.println("Max Value " + maxValue + " is associated with " + mKey + " key");

Majority Element/ max element in the map :

public class Main {
     public static void main(String[] args) {
     int[] a = {1,3,4,3,4,3,2,3,3,3,3,3};
     List<Integer> list = Arrays.stream(a).boxed().collect(Collectors.toList());
     Map<Integer, Long> map = list.parallelStream()
             .collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));
     System.out.println("Map => " + map);
     //{1=1, 2=1, 3=8, 4=2}
     map.entrySet()
     .stream()
     .max(Comparator.comparing(Entry::getValue))//compare the values and get the maximum value
     .map(Entry::getKey)// get the key appearing maximum number of times
     .ifPresentOrElse(System.out::println,() -> new RuntimeException("no such thing"));

     /*
      * OUTPUT : Map => {1=1, 2=1, 3=8, 4=2} 
      * 3
      */
     // or in  this way 
     System.out.println(".............");
     Integer maxAppearedElement = map.entrySet()
             .parallelStream()
             .max(Comparator.comparing(Entry::getValue))
             .map(Entry::getKey)
             .get();
     System.out.println(maxAppearedElement);

     } 
}

For my project, I used a slightly modified version of Jon's and Fathah's solution. In the case of multiple entries with the same value, it returns the last entry it finds:

public static Entry<String, Integer> getMaxEntry(Map<String, Integer> map) {        
    Entry<String, Integer> maxEntry = null;
    Integer max = Collections.max(map.values());

    for(Entry<String, Integer> entry : map.entrySet()) {
        Integer value = entry.getValue();

        if(null != value && max == value) {
            maxEntry = entry;
        }
    }

    return maxEntry;
}

This is going to return the keys with max value in a Map<Integer, Integer>

public Set<Integer> getMaxKeys(Map<Integer, Integer> map) { 

        if (map.isEmpty()) {
            return Collections.emptySet();
        }

        return map
        .entrySet()
        .stream()
        .collect(
            groupingBy(
                Map.Entry::getValue, TreeMap::new, mapping(Map.Entry::getKey, toSet())
            )
         )
         .lastEntry()
         .getValue();
    }

Kotlin:

val key = map.toList().groupingBy { it }.eachCount().maxByOrNull { it.value }?.key

    int max = 0;
// here m is a HashMap<String, Integer>
    for(Map.Entry<String,Integer> entry : m.entrySet()){

       if(entry.getValue() > max){
          max = entry.getValue();              
       }
    }

you can do like that

HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
hm.put(1,10);
hm.put(2,45);
hm.put(3,100);
Iterator<Integer> it = hm.keySet().iterator();
Integer fk = it.next();
Integer max = hm.get(fk);
while(it.hasNext()) {
    Integer k = it.next();
    Integer val = hm.get(k);
    if (val > max){
         max = val;
         fk=k;
    }
}
System.out.println("Max Value "+max+" is associated with "+fk+" key");

The simplest way is:

Collections.max(hmap.values());