Finding Key associated with max Value in a Java Map

Question

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

User · Answer

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   gt  maxValue                maxKey   i          maxValue   birds get i

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Is this solution ok   int   a     1  2  3  4  5  6  7  7  7  7    Map lt Integer  Integer gt  map   new HashMap lt Integer  Integer gt     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

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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 lt Integer gt  list   Arrays stream a  boxed   collect Collectors toList          Map lt Integer  Long gt  map   list parallelStream                 collect Collectors groupingBy Function identity   Collectors counting           System out println  Map   gt      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    - gt  new RuntimeException  no such thing                      OUTPUT   Map   gt   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

User · Answer

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 lt Entry lt Double Integer gt  gt                                  Override                             public int compare Entry lt Integer  Integer gt  o1  Entry lt Integer  Integer gt  o2                                    return o1 getValue    gt  o2 getValue    1 -1                                                           getKey

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1  Using Stream  public  lt K  V extends Comparable lt V gt  gt  V maxUsingStreamAndLambda Map lt K  V gt  map        Optional lt Entry lt K  V gt  gt  maxEntry   map entrySet            stream            max  Entry lt K  V gt  e1  Entry lt K  V gt  e2  - gt  e1 getValue                compareTo e2 getValue                    return maxEntry get   getKey        2  Using Collections max    with a Lambda Expression      public  lt K  V extends Comparable lt V gt  gt  V maxUsingCollectionsMaxAndLambda Map lt K  V gt  map            Entry lt K  V gt  maxEntry   Collections max map entrySet     Entry lt K  V gt  e1  Entry lt K  V gt  e2  - gt  e1 getValue                compareTo e2 getValue              return maxEntry getKey            3  Using Stream with Method Reference      public  lt K  V extends Comparable lt V gt  gt  V maxUsingStreamAndMethodReference Map lt K  V gt  map            Optional lt Entry lt K  V gt  gt  maxEntry   map entrySet                stream                max Comparator comparing Map Entry  getValue            return maxEntry get                getKey            4  Using Collections max        public  lt K  V extends Comparable lt V gt  gt  V maxUsingCollectionsMax Map lt K  V gt  map            Entry lt K  V gt  maxEntry   Collections max map entrySet    new Comparator lt Entry lt K  V gt  gt                  public int compare Entry lt K  V gt  e1  Entry lt K  V gt  e2                    return e1 getValue                        compareTo e2 getValue                                       return maxEntry getKey            5  Using Simple Iteration  public  lt K  V extends Comparable lt V gt  gt  V maxUsingIteration Map lt K  V gt  map        Map Entry lt K  V gt  maxEntry   null      for  Map Entry lt K  V gt  entry   map entrySet              if  maxEntry    null    entry getValue                compareTo maxEntry getValue     gt  0                maxEntry   entry                      return maxEntry getKey

User · Answer

Java 8 way to get all keys with max value   Integer max   PROVIDED MAP entrySet                stream                max  entry1  entry2  - gt  entry1 getValue    gt  entry2 getValue     1   -1               get                getValue     List listOfMax   PROVIDED MAP entrySet                stream                filter entry - gt  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

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A simple one liner using Java-8   Key key   Collections max map entrySet    Map Entry comparingByValue    getKey

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This is going to return the keys with max value in a Map lt Integer  Integer gt  public Set lt Integer gt  getMaxKeys Map lt Integer  Integer gt  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

User · Answer

int maxValue   0  int mKey   0  for Integer key  map keySet         if map get key   gt  maxValue           maxValue   map get key           mKey   key          System out println  Max Value     maxValue     is associated with     mKey     key

User · Answer

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

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given map  HashMap abc   new HashMap lt       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 - gt  entry getValue      Collections max abc values       if only want to get the keys for the filter map   abc entrySet           stream           filter entry - gt  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 - gt  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 - gt  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 - gt  entry getValue      Collections max abc values        map Map Entry  getvalue     collect Collectors toList

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you can do like that  HashMap lt Integer Integer gt  hm   new HashMap lt Integer Integer gt     hm put 1 10   hm put 2 45   hm put 3 100   Iterator lt Integer gt  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  gt  max            max   val           fk k          System out println  Max Value   max   is associated with   fk   key

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For completeness  here is a java-8 way of doing it  countMap entrySet   stream   max  entry1  entry2  - gt  entry1 getValue    gt  entry2 getValue     1   -1  get   getKey      or  Collections max countMap entrySet     entry1  entry2  - gt  entry1 getValue   - entry2 getValue    getKey      or  Collections max countMap entrySet    Comparator comparingInt Map Entry  getValue   getKey

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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 lt Foo  Bar gt  maxEntry   null   for  Map Entry lt Foo  Bar gt  entry   map entrySet          if  maxEntry    null    entry getValue   compareTo maxEntry getValue     gt  0                maxEntry   entry

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This code will print all the keys with maximum value  public class NewClass4       public static void main String   args                HashMap lt Integer Integer gt map new HashMap lt Integer  Integer gt             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 lt Integer  Integer gt  entry   map entrySet          Itrate through hashmap             if  entry getValue    maxValueInMap                    System out println entry getKey            Print the key with max value

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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 lt String  Integer gt  getMaxEntry Map lt String  Integer gt  map                Entry lt String  Integer gt  maxEntry   null      Integer max   Collections max map values          for Entry lt String  Integer gt  entry   map entrySet              Integer value   entry getValue             if null    value  amp  amp  max    value                maxEntry   entry                       return maxEntry

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I have two methods  using this m  thod to get the key with the max value    public static Entry lt String  Integer gt  getMaxEntry Map lt String  Integer gt  map               Entry lt String  Integer gt  maxEntry   null      Integer max   Collections max map values          for Entry lt String  Integer gt  entry   map entrySet              Integer value   entry getValue            if null    value  amp  amp  max    value                maxEntry   entry                      return maxEntry      As an example gettin the Entry with the max value using the method     Map Entry lt String  Integer gt  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

[java] Finding Key associated with max Value in a Java Map

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