How to count frequency of characters in a string

Question

I need to write some kind of loop that can count the frequency of each letter in a string   For example   aasjjikkk  would count 2  a   1  s   2  j   1  i   3  k   Ultimately id like these to end up in a map with the character as the key and the count as the value  Any good idea how to do this

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import java io FileInputStream  import java util HashSet  import java util Iterator  public class CountFrequencyOfCharater   public static void main String args    throws Exception       HashSet hs new HashSet        String str  hey how are you        char arr   new char str length         for int i 0 i lt str length   i                  arr i  str charAt i             for int j 0 j lt str length   j                  int c 0          for int k 0 k lt str length   k                          if arr j   arr k               c                      hs add arr j      c                     Iterator it hs iterator            while it hasNext                           System out print it next

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You can use a Multiset  from guava   It will give you the count for each object  For example   Multiset lt Character gt  chars   HashMultiset create    for  int i   0  i  lt  string length    i          chars add string charAt i        Then for each character you can call chars count  a   and it returns the number of occurrences

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Well  two ways come to mind and it depends on your preference    Sort the array by characters  Then  counting each character becomes trivial  But you will have to make a copy of the array first  Create another integer array of size 26  say freq  and str is the array of characters   for int i   0  i  lt  str length  i      freq str i  -  a         Assuming all characters are in lower case   So the number of  a   s will be stored at freq 0  and the number of  z   s will be at freq 25

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Since there was no Java 8 solution  thought of posting one  Also  this solution is much neater  readable and concise than some of the other solutions mentioned here   String string    aasjjikkk    Map lt Character  Long gt  characterFrequency   string chars       creates an IntStream      mapToObj c - gt   char  c     converts the IntStream to Stream lt Character gt       collect Collectors groupingBy c - gt  c  Collectors counting         creates a                                                                        Map lt Character  Long gt                                                                          where the Long is                                                                        the frequency

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If this does not need to be super-fast just create an array of integers  one integer for each letter  only alphabetic so 2 26 integers  or any binary data possible    go through the string one char at a time  get the index of the responsible integer  e g  if you only have alphabetic chars you can have  A  be at index 0 and get that index by subtracting any  A  to  Z  by  A  just as an example of how you can get reasonably fast indices  and increment the value in that index   There are various micro-optimizations to make this faster  if necessary

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String s    aaaabbbbcccddddd   Map lt Character  Integer gt  map   new HashMap lt  gt       Using one line in Java8  s chars   forEach e- gt map put  char e  map getOrDefault  char e  0    1

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package com rishi zava   import java util HashMap  import java util Map  import java util Map Entry   public class ZipString       public static void main String arg              String input    aaaajjjgggtttssvvkkllaaiiikk           int len   input length            Map lt Character  Integer gt  zip   new HashMap lt Character  Integer gt             for  int j   0  len  gt  j  j                  int count   0              for  int i   0  len  gt  i  i                      if  input charAt j     input charAt i                         count                                                zip put input charAt j   count                     StringBuffer myValue   new StringBuffer            String myMapKeyValue               for  Entry lt Character  Integer gt  entry   zip entrySet                  myMapKeyValue   Character toString entry getKey    concat                      Integer toString entry getValue                  myValue append myMapKeyValue                     System out println myValue             Input   aaaajjjgggtttssvvkkllaaiiikk  Output   a6s2t3v2g3i3j3k4l2

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There is one more option and it looks quite nice  Since java 8 there is new method merge java doc    public static void main String   args        String s    aaabbbcca        Map lt Character  Integer gt  freqMap   new HashMap lt  gt         for  int i   0  i  lt  s length    i              Character c   s charAt i           freqMap merge c  1   a  b  - gt  a   b             freqMap forEach  k  v  - gt  System out println k     and     v        Or even cleaner with ForEach         for  Character c   s toCharArray                  freqMapSecond merge c  1  Integer  sum

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You can use a CharAdapter and a CharBag from Eclipse Collections and avoid boxing to Character and Integer   CharBag bag   Strings asChars  aasjjikkk   toBag     Assert assertEquals 2  bag occurrencesOf  a     Assert assertEquals 1  bag occurrencesOf  s     Assert assertEquals 2  bag occurrencesOf  j     Assert assertEquals 1  bag occurrencesOf  i     Assert assertEquals 3  bag occurrencesOf  k       Note  I am a committer for Eclipse Collections

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Using the stream API as of JDK-8   Map lt Character  Long gt  frequency               str chars                   mapToObj c - gt   char c                  collect Collectors groupingBy Function identity    Collectors counting        or if you want the keys as Integers   Map lt Character  Integer gt  frequency               str chars                   mapToObj c - gt   char c                  collect Collectors groupingBy Function identity    Collectors summingInt c - gt  1       Another variant   Map lt Character  Integer gt  frequency                str chars                   mapToObj c - gt   char c                  collect Collectors toMap Function identity    c - gt  1  Math  addExact

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A concise way to do this is   Map lt Character Integer gt  frequencies   new HashMap lt  gt     for  char ch   input toCharArray        frequencies put ch  frequencies getOrDefault ch  0    1     We use a for-each to loop through every character  The frequencies getOrDefault   gets value if key is present or returns as default  its second argument

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This is more Effective way to count frequency of characters in a string  public class demo       public static void main String   args            String s    babdcwertyuiuygf           Map lt Character  Integer gt  map   new TreeMap lt  gt             s chars   forEach e- gt map put  char e  map getOrDefault  char e  0    1            StringBuffer myValue   new StringBuffer            String myMapKeyValue               for  Map Entry lt Character  Integer gt  entry   map entrySet                  myMapKeyValue   Character toString entry getKey    concat                  Integer toString entry getValue                  myValue append myMapKeyValue                     System out println myValue

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We can use frequency method of Collections class for this  Split the string into string array  Use HashSet to remove duplicates and check frequency of each object in HashSet using frequency method of Collections  void usingCollections       String input    cuttack      String    stringArray   input split         Set lt String gt  s   new HashSet Arrays asList stringArray       for String abc   s        System out println  abc       Collections frequency Arrays asList stringArray  abc

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This is similar to xunil154 s answer  except that a string is made a char array and a linked hashmap is used to maintain the insertion order of the characters   String text    aasjjikkk   char   charArray   text toCharArray    Map lt Character  Integer gt  freqList   new LinkedHashMap lt Character  Integer gt              for char key   charArray                if freqList containsKey key                    freqList put key  freqList get key    1                 else                 freqList put key  1

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import java util HashMap  import java util Iterator  import java util Map  import java util Map Entry  import java util Scanner    public class FrequenceyOfCharacters        public static void main String   args            System out println  quot Please enter the string to count each character frequencey   quot            Scanner sc new  Scanner System in           String s  sc nextLine            String input   s replaceAll  quot   s quot   quot  quot       To remove space          frequenceyCount input                                private static void frequenceyCount String input                     Map lt Character Integer gt  hashCount new HashMap lt  gt             Character c          for int i 0  i lt input length   i                         c  input charAt i              if hashCount get c   null                  hashCount put c  hashCount get c  1               else                 hashCount put c  1                                  Iterator it   hashCount entrySet   iterator            System out println  quot char   frequency quot            while  it hasNext                  Map Entry pairs    Map Entry it next                System out println pairs getKey      quot     quot    pairs getValue                 it remove

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Here is another solution  dodgy as it may be   public char getNumChar String s        char   c   s toCharArray        String alphabet    abcdefghijklmnopqrstuvwxyz       int   countArray   new int 26       for  char x   c            for  int i   0  i  lt  alphabet length    i                  if  alphabet charAt i     x                    countArray i                                        java util HashMap lt Integer  Character gt  countList   new java util HashMap lt Integer  Character gt          for  int i   0  i  lt  26  i              countList put countArray i   alphabet charAt i              java util Arrays sort countArray       int max   countArray 25       return countList get max

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import java util    class Charfrequency    public static void main String a              Scanner sc new Scanner System in           System out println  Enter Your String              String s1 sc nextLine            int count j 1          char var  a           char ch   s1 toCharArray            while j lt  26                       count 0                  for int i 0  i lt s1 length    i                                          if ch i   var    ch i   var-32                                                count                                                            if count gt 0                   System out println  Frequency of   var   is   count                                     var                    j

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The shorted possible code using a HashMap   With no forceful line saves   private static Map lt Character  Integer gt  findCharacterFrequency String str             Map lt Character  Integer gt  map   new HashMap lt  gt              for  char ch   str toCharArray                     Using getOrDefault    since Java1 8                map put ch  map getOrDefault ch  0    1                     return map

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From C language   include lt stdio h gt     include  lt string h gt     int main         char s 1000         int  i j k count 0 n      printf  quot Enter  the string    quot        gets s       for j 0 s j  j         n j       printf  quot  frequency count character in string  n quot        for i 0 i lt n i                    count 1          if s i                                for j i 1 j lt n j                                              if s i   s j                                  count                     s j    0                                         printf  quot    c     d  n quot  s i  count                       return 0

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Please try the given code below  hope it will helpful to you       import java util Scanner   class String55       public static int frequency String s1 String s2                 int count 0          char ch   s1 toCharArray            char ch1   s2 toCharArray            for  int i 0 i lt ch length-1  i                                 int k i                   int j1 i 1                  int j 0                  int j11 j                  int j2 j 1                                        while k lt ch length  amp  amp  j11 lt ch1 length  amp  amp  ch k   ch1 j11                                             k                        j11                                             int l k j1                  int m j11 j2                  if  l   m                                        count 1                      count                                                       return count              public static void main  String   args            Scanner sc new Scanner System in           System out println  enter the pattern            String s1 sc next                System out println  enter the String                String s2 sc next                int res frequency s1  s2               System out println  FREQUENCY     res              SAMPLE OUTPUT  enter the pattern man enter the String dhimanman FREQUENCY  2  Thank-you Happy coding

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You can use a Hashtable with each character as the key and the total count becomes the value   Hashtable lt Character Integer gt  table   new Hashtable lt Character Integer gt     String str    aasjjikkk   for  c in str         if  table get c     null           table put c 1       else         table put c table get c    1      for  elem in table         println  elem     elem

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You can use a java Map and map a char to an int  You can then iterate over the characters in the string and check if they have been added to the map  if they have  you can then increment its value   For example   HashMap lt Character  Integer gt  map   new HashMap lt Character  Integer gt     String s    aasjjikkk   for  int i   0  i  lt  s length    i          char c   s charAt i       Integer val   map get c       if  val    null            map put c  new Integer val   1              else          map put c  1            At the end you will have a count of all the characters you encountered and you can extract their frequencies from that   Alternatively  you can use Bozho s solution of using a Multiset and counting the total occurences

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Another way using map merge method     Map lt Character  Integer gt  map   new HashMap lt  gt        String s    aasjjikkk       for  int i   0  i  lt  s length    i              map merge s charAt i   1   l  r  - gt  l   r

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import java util ArrayList  import java util Collections   public class Freq        public static void main String   args               TODO Auto-generated method stub         String temp  zsaaqaaaaaaaabbbbbcc       List lt String gt  temp1  new ArrayList lt String gt          ArrayList lt Integer gt freq new ArrayList lt Integer gt         for int i 0 i lt temp length  -1 i                         temp1 add Character toString temp charAt i                     Set lt String gt  uniqset new HashSet lt String gt  temp1       for String s uniqset                freq add Collections frequency temp1  s            System out println s   -- gt  gt   Collections frequency temp1  s                              ------Output-------        a -- gt  gt 10        b -- gt  gt 5        c -- gt  gt 1        q -- gt  gt 1        s -- gt  gt 1        z -- gt  gt 1   Use collections frequency method to count frequency of char

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package com dipu string   import java util HashMap  import java util Map   public class RepetativeCharInString       public static void main String   args            String data    aaabbbcccdddffffrss           char   charArray   data toCharArray            Map lt Character  Integer gt  map   new HashMap lt  gt             for  char c   charArray                if  map containsKey c                     map put c  map get c    1                 else                   map put c  1                                   System out println map

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Here is a solution   Define your own Pair   public class Pair       private char letter      private int count      public Pair char letter  int count                this letter   letter          this count  count            public char getLetter   return key       public int getCount   return count       Then you could do   public static Pair countCharFreq String s        String temp   s      java util List lt Pair gt  list   new java util ArrayList lt Pair gt         while temp length      0                list add new Pair temp charAt 0   countOccurrences temp  temp charAt 0              temp replaceAll       temp charAt 0                     public static int countOccurrences String s  char c        int count   0      for int i   0  i  lt  s length    i                  if s charAt i     c  count              return count

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Uffh  Don t you think this is the simplest solution       char inputChar            int freq     fd fdfd f dfd fd  replaceAll        inputChar           length        System out println  freq     freq

[java] How to count frequency of characters in a string?

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