Finding Key associated with max Value in a Java Map
JavaHashmapJava Problem Overview
What is the easiest way to get key associated 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.
Java Solutions
Solution 1 - Java
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;
}
}
Solution 2 - Java
For completeness, here is a [tag: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();
Solution 3 - Java
A simple one liner using Java-8
Key key = Collections.max(map.entrySet(), Map.Entry.comparingByValue()).getKey();
Solution 4 - Java
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
}
}
}
}
Solution 5 - Java
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();
Solution 6 - Java
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();
}
Solution 7 - Java
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);
Solution 8 - Java
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);
Solution 9 - Java
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);
}
}
Solution 10 - Java
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()
Solution 11 - Java
given map
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())
Solution 12 - Java
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);
Solution 13 - Java
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");
Solution 14 - Java
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);
}
}
Solution 15 - Java
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;
}
Solution 16 - Java
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();
}
Solution 17 - Java
Kotlin:
val key = map.toList().groupingBy { it }.eachCount().maxByOrNull { it.value }?.key
Solution 18 - Java
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();
}
}
Solution 19 - Java
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");
Solution 20 - Java
The simplest way is:
Collections.max(hmap.values());