How to sort a HashMap in Java

Question

How are we able to sort a HashMap lt key  ArrayList gt    I want to sort on the basis of a value in the ArrayList

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Sorted List by hasmap keys   SortedSet lt String gt  keys   new TreeSet lt String gt  myHashMap keySet       Sorted List by hashmap values   SortedSet lt String gt  values   new TreeSet lt String gt  myHashMap values       In case of duplicated map values   List lt String gt  mapValues   new ArrayList lt String gt  myHashMap values     Collections sort mapValues     Good Luck

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have you considered using a LinkedHashMap lt           public static void main String   args        Map lt Object  Object gt  handler   new LinkedHashMap lt Object  Object gt         handler put  item    Value        handler put 2   Movies        handler put  isAlive   true        for  Map Entry lt Object  Object gt  entrY   handler entrySet            System out println entrY getKey       gt  gt     entrY getValue          List lt Map Entry lt String  Integer gt  gt  entries   new ArrayList lt Map Entry lt String  Integer gt  gt         Collections sort entries  new Comparator lt Map Entry lt String  Integer gt  gt              public int compare Map Entry lt String  Integer gt  a                  Map Entry lt String  Integer gt  b                return a getValue   compareTo b getValue                           results into an organized linked object    item gt  gt Value  2 gt  gt Movies  isAlive gt  gt true   check the sorting part picked from here

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Convert hashmap to a ArrayList with a pair class  Hashmap lt Object Object gt  items   new HashMap lt  gt       to  List lt Pair lt Object Object gt  gt  items   new ArrayList lt  gt       so you can sort it as you want  or list sorted by adding order

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Sorting by key   public static void main String   args        Map lt String String gt  map   new HashMap lt  gt          map put  b    dd        map put  c    cc        map put  a    aa         map   new TreeMap lt  gt  map        for  String key   map keySet              System out println key     map get key

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Without any more information  it s hard to know exactly what you want  However  when choosing what data structure to use  you need to take into account what you need it for  Hashmaps are not designed for sorting - they are designed for easy retrieval  So in your case  you d probably have to extract each element from the hashmap  and put them into a data structure more conducive to sorting  such as a heap or a set  and then sort them there

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In Java 8   Comparator lt Entry lt String  Item gt  gt  valueComparator         e1  e2  - gt  e1 getValue   getField   compareTo e2 getValue   getField      Map lt String  Item gt  sortedMap        unsortedMap entrySet   stream        sorted valueComparator       collect Collectors toMap Entry  getKey  Entry  getValue                                e1  e2  - gt  e1  LinkedHashMap  new      Using Guava   Map lt String  Item gt  map        Function lt Item  Integer gt  getField   new Function lt Item  Integer gt          public Integer apply Item item            return item getField       the field to sort on          comparatorFunction   Functions compose getField  Functions forMap map    comparator   Ordering natural   onResultOf comparatorFunction   Map lt String  Item gt  sortedMap   ImmutableSortedMap copyOf map  comparator

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A proper answer   HashMap lt Integer  Object gt  map   new HashMap lt Integer  Object gt      ArrayList lt Integer gt  sortedKeys   new ArrayList lt Integer gt  map keySet     Collections sort sortedKeys  new Comparator lt Integer gt         Override   public int compare Integer a  Integer b        return a compareTo b            for  Integer key  sortedKeys        map get key       Note that HashMap itself cannot maintain sorting  as other answers have pointed out  It s a hash map  and hashed values are unsorted  You can thus either sort the keys when you need to and then access the values in order  as I demonstrated above  or you can find a different collection to store your data  like an ArrayList of Pairs Tuples  such as the Pair found in Apache Commons   https   commons apache org proper commons-lang apidocs org apache commons lang3 tuple Pair html

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If you want to combine a Map for efficient retrieval with a SortedMap  you may use the ConcurrentSkipListMap   Of course  you need the key to be the value used for sorting

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Do you have to use a HashMap  If you only need the Map Interface use a TreeMap    If you want to sort by comparing values in the HashMap  You have to write code to do this  if you want to do it once you can sort the values of your HashMap   Map lt String  Person gt  people   new HashMap lt  gt     Person jim   new Person  Jim   25   Person scott   new Person  Scott   28   Person anna   new Person  Anna   23    people put jim getName    jim   people put scott getName    scott   people put anna getName    anna       not yet sorted List lt Person gt  peopleByAge   new ArrayList lt  gt  people values      Collections sort peopleByAge  Comparator comparing Person  getAge     for  Person p   peopleByAge        System out println p getName       t    p getAge         If you want to access this sorted list often  then you could insert your elements into a HashMap lt TreeSet lt Person gt  gt   though the semantics of sets and lists are a bit different

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I have developed a class which can be used to sort a map on the basis of keys and values  The basic idea is if you have sort a map using keys then create a TreepMap from your Map which will sort the map by keys  And in case of sorting by values create a list from entrySet and sort the list using comparator interface   Here is the full solution    public static void main String   args        Map lt String  Integer gt  unSortedMap   new LinkedHashMap lt String  Integer gt         unSortedMap put  A   2       unSortedMap put  V   1       unSortedMap put  G   5       System out println  Unsorted Map   n        for  Map Entry lt String  Integer gt  entry   unSortedMap entrySet              System out println entry getKey             entry getValue               System out println   n        System out println  Sorting Map Based on Keys   n        Map lt String  Integer gt  keySortedMap   new TreeMap lt String  Integer gt  unSortedMap       for  Map Entry lt String  Integer gt  entry   keySortedMap entrySet              System out println entry getKey             entry getValue               System out println   n        System out println  Sorting Map Based on Values   n        List lt Entry lt String  Integer gt  gt  entryList   new ArrayList lt Entry lt String  Integer gt  gt  unSortedMap entrySet         Collections sort entryList  new Comparator lt Entry lt String  Integer gt  gt                Override         public int compare Entry lt String  Integer gt  obj1  Entry lt String  Integer gt  obj2                return obj1 getValue   compareTo obj2 getValue                           unSortedMap clear        for  Entry lt String  Integer gt  entry   entryList            unSortedMap put entry getKey    entry getValue             System out println entry getKey             entry getValue               Code is properly tested  D

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Sorting HashMap by value in Java   public class HashMapSortByValue       public static void main String   args             HashMap lt Long String gt  unsortMap   new HashMap lt Long String gt                 unsortMap put 5l  B                unsortMap put 8l  A                unsortMap put 2l   D                unsortMap put 7l  C                  System out println  Before sorting                      System out println unsortMap                HashMap lt Long String gt  sortedMapAsc   sortByComparator unsortMap               System out println  After sorting                      System out println sortedMapAsc               public static HashMap lt Long String gt  sortByComparator              HashMap lt Long String gt  unsortMap                 List lt Map Entry lt Long String gt  gt  list   new LinkedList lt Map Entry lt Long String gt  gt                   unsortMap entrySet                  Collections sort list  new Comparator lt Map Entry lt Long String gt  gt                       public int compare Map Entry lt Long String gt  o1  Map Entry lt Long String gt  o2                        return o1 getValue   compareTo o2 getValue                                                    HashMap lt Long String gt  sortedMap   new LinkedHashMap lt Long String gt                 for  Entry lt Long String gt  entry   list                  sortedMap put entry getKey    entry getValue                               return sortedMap

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Seems like you might want a treemap   http   docs oracle com javase 7 docs api java util TreeMap html  You can pass in a custom comparator to it if that applies

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HashMap doesnt maintain any order  so if you want any kind of ordering  you need to store that in something else  which is a map and can have some kind of ordering  like LinkedHashMap  below is a simple program  by which you can sort by key  value  ascending  descending     if you modify the compactor  you can use any kind of ordering  on keys and values   package com edge collection map   import java util Collections  import java util Comparator  import java util HashMap  import java util LinkedHashMap  import java util LinkedList  import java util List  import java util Map  import java util Map Entry   public class SortMapByKeyValue   Map lt String  Integer gt  map   new HashMap lt String  Integer gt      public static void main String   args         SortMapByKeyValue smkv   new SortMapByKeyValue        smkv createMap         System out println  After sorting by key ascending order              smkv sortByKey true        System out println  After sorting by key descindeng order              smkv sortByKey false        System out println  After sorting by value ascending order              smkv sortByValue true        System out println  After sorting by value  descindeng order              smkv sortByValue false       void createMap         map put  B   55       map put  A   80       map put  D   20       map put  C   70       map put  AC   70       map put  BC   70       System out println  Before sorting              printMap map      void sortByValue boolean order         List lt Entry lt String  Integer gt  gt  list   new LinkedList lt Entry lt String  Integer gt  gt  map entrySet         Collections sort list  new Comparator lt Entry lt String  Integer gt  gt              public int compare Entry lt String  Integer gt  o1  Entry lt String  Integer gt  o2                if  order                    return o1 getValue   compareTo o2 getValue                   else                   return o2 getValue   compareTo o1 getValue                                          Map lt String  Integer gt  sortedMap   new LinkedHashMap lt String  Integer gt         for  Entry lt String  Integer gt  entry   list            sortedMap put entry getKey    entry getValue               printMap sortedMap       void sortByKey boolean order         List lt Entry lt String  Integer gt  gt  list   new LinkedList lt Entry lt String  Integer gt  gt  map entrySet         Collections sort list  new Comparator lt Entry lt String  Integer gt  gt              public int compare Entry lt String  Integer gt  o1  Entry lt String  Integer gt  o2                if  order                    return o1 getKey   compareTo o2 getKey                   else                   return o2 getKey   compareTo o1 getKey                                          Map lt String  Integer gt  sortedMap   new LinkedHashMap lt String  Integer gt         for  Entry lt String  Integer gt  entry   list            sortedMap put entry getKey    entry getValue               printMap sortedMap      public void printMap Map lt String  Integer gt  map           System out println map       for  Entry lt String  Integer gt  entry   map entrySet              System out println entry getKey             entry getValue                 here is the git link

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http   snipplr com view 2789 sorting-map-keys-by-comparing-its-values   get the keys  List keys   new ArrayList yourMap keySet       Sort them   Collections sort keys    print them   In any case  you can t have sorted values in HashMap  according to API This class makes no guarantees as to the order of the map  in particular  it does not guarantee that the order will remain constant over time      Though you can push all these values to LinkedHashMap  for later use as well

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Custom compare function which includes functionality for the Turkish alphabet or other different languages than english    public  lt K extends Comparable V extends Comparable gt  LinkedHashMap lt K V gt  sortByKeys LinkedHashMap lt K V gt  map       List lt K gt  keys   new LinkedList lt K gt  map keySet         Collections sort keys   Comparator lt   super K gt   new Comparator lt String gt               Override         public int compare String first  String second                Collator collator   Collator getInstance Locale getDefault                   Collator collator   Collator getInstance new Locale  tr    TR                 return collator compare first  second                          LinkedHashMap lt K V gt  sortedMap   new LinkedHashMap lt K V gt         for K key  keys           sortedMap put key  map get key               return sortedMap      here is the using example as the following  LinkedHashMap lt String  Boolean gt  ligList   new LinkedHashMap lt String  Boolean gt     ligList   sortByKeys ligList

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Sorting HashMap by Value   As others have pointed out  HashMaps are for easy lookups if you change that or try to sort inside the map itself you will no longer have O 1  lookup   The code for your sorting is as follows   class Obj implements Comparable lt Obj gt       String key      ArrayList lt Integer gt  val      Obj String key  ArrayList lt Integer gt  val            this key key      this val val            public int compareTo Obj o                Write your sorting logic here        this val compared to o val        return 0           public void sortByValue Map lt String  ArrayList lt  gt  gt  mp        ArrayList lt Obj gt  arr new ArrayList lt Obj gt         for String z mp keySet     Make an object and store your map into the arrayList                Obj o new Obj z mp get z            arr add o             System out println arr    Unsorted     Collections sort arr     This sorts based on the conditions you coded in the compareTo function      System out println arr    Sorted

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I developed a fully tested working solution  Hope it helps  import java io BufferedReader  import java io IOException  import java util ArrayList  import java util Collections  import java util Comparator  import java util HashMap  import java util List  import java util StringTokenizer    public class Main       public static void main String   args        try           BufferedReader in   new BufferedReader new java io InputStreamReader            System in                String str           HashMap lt Integer  Business gt  hm   new HashMap lt Integer  Business gt             Main m   new Main              while   str   in readLine       null                  StringTokenizer st   new StringTokenizer str               int id   Integer parseInt st nextToken           first integer             int rating   Integer parseInt st nextToken           second               Business a   m new Business id  rating                 hm put id  a                 List lt Business gt  ranking   new ArrayList lt Business gt  hm values                  Collections sort ranking  new Comparator lt Business gt                       public int compare Business i1  Business i2                        return i2 getRating   - i1 getRating                                                   for  int k 0 k lt ranking size   k                      System out println  ranking get k  getId            ranking get k   getRating                                        in close           catch  IOException e            e printStackTrace              public class Business       Integer id      Integer rating       public Business int id2  int rating2                id id2          rating rating2              public Integer getId                 return id            public Integer getRating                 return rating

[java] How to sort a HashMap in Java

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