Java count occurrence of each item in an array

Question

Is there any method for counting the occurrence of each item on an array   Lets say I have   String   array     name1   name2   name3   name4    name5      Here the output will be   name1 1 name2 1 name3 1 name4 1 name5 1   and if I have   String   array     name1   name1   name2   name2    name2      The output would be   name1 2 name2 3   The output here is just to demonstrate the expected result

User · Answer

I wrote a solution for this to practice myself  It doesn t seem nearly as awesome as the other answers posted  but I m going to post it anyway  and then learn how to do this using the other methods as well  Enjoy   public static Integer   countItems String   arr        List lt Integer gt  itemCount   new ArrayList lt Integer gt         Integer counter   0      String lastItem   arr 0        for int i   0  i  lt  arr length  i                  if arr i  equals lastItem                         counter                      else                       itemCount add counter               counter   1                    lastItem   arr i             itemCount add counter        return itemCount toArray new Integer itemCount size         public static void main String   args        String   array     name1   name1   name2   name2    name2    name3                name1   name1   name2   name2    name2    name3        Arrays sort array       Integer   cArr   countItems array       int num   0      for int i   0  i  lt  cArr length  i                  num    cArr i -1          System out println array num           cArr i  toString

User · Answer

An Answer w o using Hashset or map or Arraylist  public class Count       static String names       name1   name1   name2   name2    name2        public static void main String args               printCount names               public static void printCount String   names            java util Arrays sort names           int n   names length  c          for int i 0 i lt n i                 System out print names i                          System out println            int result     new int n           for int i 0 i lt n i                 result i    0                     for int i  0 i lt n i                 if  i    n-1                   for int j 0 j lt n j                         if names i     names j                            result i                                                 else if  names n-2     names n-1                result i    result i-1                        else result i    1                    int max   0 index   0          for int i 0 i lt n i              System out print result i                        if  result i   gt   max                   max   result i                   index   i

User · Answer

You could use a MultiSet from Google Collections Guava or a Bag from Apache Commons   If you have a collection instead of an array  you can use addAll   to add the entire contents to the above data structure  and then apply the count   method to each value  A SortedMultiSet or SortedBag would give you the items in a defined order   Google Collections actually has very convenient ways of going from arrays to a SortedMultiset

User · Answer

There are several methods which can help  but this is one is using for loop   import java util Arrays   public class one dimensional for    private static void count int   arr         Arrays sort arr        int sum   0  counter   0       for  int i   0  i  lt  arr length  i              if  arr 0     arr arr length - 1                 System out println arr 0           counter     times                break            else               if  i     arr length - 1                     sum    arr arr length - 1                   counter                    System out println  sum   counter            counter                             times                    break                else                   if  arr i     arr i   1                         sum    arr i                       counter                      else if  arr i     arr i   1                         sum    arr i                       counter                        System out println  sum   counter            counter                                 times                        sum   0                      counter   0                                                     public static void main String   args        int nums       1  1  1  1  2  2  2  3  3  4  5  5  5  5  6        count nums

User · Answer

List asList   Arrays asList array   Set lt String gt  mySet   new HashSet lt String gt  asList    for String s  mySet    System out println s    quot   quot    Collections frequency asList s

User · Answer

you can find using HashMap with simple technic  public class HashMapExample       public static void main String   args            stringArray                    public static void stringArray         String   a     name1   name2   name3   name4    name5         Map lt String  String gt  hm   new HashMap lt String  String gt         for int i 0 i lt a length i              String bl  String hm get a i        if bl  null                hm put a i  String valueOf 1         else               String k hm get a i            int j Integer valueOf k           hm put a i  String valueOf j 1                       hm entrySet        System out println  map elements are   hm toString

User · Answer

Using HashMap it is walk in the park    main        String   array    a   ab   a   abc   abc   a   ab   ab   a        Map lt String Integer gt  hm   new HashMap         for String x array            if  hm containsKey x                hm put x 1            else              hm put x  hm get x  1                       System out println hm

User · Answer

It can be done in a very simple way using collections  please find the code below  String   array     name1   name1   name2   name2    name2    List lt String gt  sampleList  List lt String gt   Arrays asList array   for String inpt array   int frequency Collections frequency sampleList inpt   System out println inpt     frequency       Here the output will be like  name1 2 name1 2 name2 3 name2 3 name2 3  To avoid printing redundant keys use HashMap and get your desired output

User · Answer

This is a simple script I used in Python but it can be easily adapted   Nothing fancy though   def occurance arr     results        for n in arr        data            data  point     n       data  count     0       for i in range 0  len arr              if n    arr i                 data  count      1       results append data    return results

User · Answer

You can use HashMap  where Key  is your string  and value - count

User · Answer

Count String occurence using hashmap  streams  amp  collections  import java util Arrays  import java util Collections  import java util HashMap  import java util HashSet  import java util List  import java util Map  import java util Set  import java util stream Collectors   public class StringOccurence    public static void main String args           String   stringArray      name1    name1    name2    name2    name2         countStringOccurence stringArray       countStringOccurenceUsingStream stringArray       countStringOccurenceUsingCollections stringArray      private static void countStringOccurenceUsingCollections String   stringArray           TODO Auto-generated method stub     List lt String gt  asList   Arrays asList stringArray       Set lt String gt  set   new HashSet lt String gt  asList       for  String string   set            System out println string       -- gt        Collections frequency asList  string              private static void countStringOccurenceUsingStream String   stringArray           TODO Auto-generated method stub     Arrays stream stringArray  collect Collectors groupingBy s - gt  s                forEach  k  v  - gt  System out println k       -- gt        v size         private static void countStringOccurence String   stringArray           TODO Auto-generated method stub     Map lt String  Integer gt  map   new HashMap lt String  Integer gt         for  String s   stringArray            if  map containsKey s                 map put s  map get s    1             else               map put s  1                        for  Map Entry lt String  Integer gt  entry   map entrySet              System out println entry getKey         -- gt        entry getValue

User · Answer

I would use a hashtable with in key takes the element of the array  here string  and in value an Integer   then go through the list doing something like this    for String s array   if hash containsKey s      Integer i   hash get s     i     else    hash put s  new Interger 1

User · Answer

With java-8  you can do it like this  String   array     quot name1 quot   quot name2 quot   quot name3 quot   quot name4 quot    quot name5 quot    quot name2 quot    Arrays stream array         collect Collectors groupingBy s - gt  s          forEach  k  v  - gt  System out println k  quot   quot  v size       Output  name5 1 name4 1 name3 1 name2 2 name1 1  What it does is   Create a Stream lt String gt  from the original array Group each element by identity  resulting in a Map lt String  List lt String gt  gt  For each key value pair  print the key and the size of the list  If you want to get a Map that contains the number of occurences for each word  it can be done doing  Map lt String  Long gt  map   Arrays stream array       collect Collectors groupingBy s - gt  s  Collectors counting       For more informations   Stream Collectors  Hope it helps

User · Answer

You can use Hash Map as given in the example below       import java util HashMap  import java util Set               author Abdul Rab Khan         public class CounterExample       public static void main String   args            String   array      name1    name1    name2    name2    name2             countStringOccurences array                         This method process the string array to find the number of occurrences of        each string element                 param strArray                   array containing string elements             private static void countStringOccurences String   strArray            HashMap lt String  Integer gt  countMap   new HashMap lt String  Integer gt             for  String string   strArray                if   countMap containsKey string                     countMap put string  1                 else                   Integer count   countMap get string                   count   count   1                  countMap put string  count                                   printCount countMap                         This method will print the occurrence of each element                 param countMap                   map containg string as a key  and its count as the value             private static void printCount HashMap lt String  Integer gt  countMap            Set lt String gt  keySet   countMap keySet            for  String string   keySet                System out println string           countMap get string

User · Answer

import java util ArrayList  import java util Arrays  import java util HashMap  import java util List   public class MultiString        public HashMap lt String  Integer gt  countIntem  String   array              Arrays sort array           HashMap lt String  Integer gt  map   new HashMap lt String  Integer gt             Integer count   0          String first   array 0           for  int counter   0  counter  lt  array length  counter                   if first hashCode      array counter  hashCode                      count   count   1                else                   map put first  count                   count   1                            first   array counter               map put first  count                      return map                         param args             public static void main String   args               TODO Auto-generated method stub         String   array      name1    name1    name2    name2    name2                    name3    name1    name1    name2    name2    name2    name3              HashMap lt String  Integer gt  countMap   new MultiString   countIntem array           System out println countMap              Gives you O n  complexity

User · Answer

You can do it by using Arrays sort and Recursion  The same wine but in a different bottle      import java util Arrays   public class ArrayTest   public static int mainCount 0   public static void main String   args        String prevItem           String   array     name1   name1   name2   name2    name2        Arrays sort array        for String item array           if   prevItem equals item                mainCount   0              countArray array  0  item               prevItem   item                     private static void countArray String   arr  int currentPos  String item        if currentPos    arr length           System out println item          mainCount           return            else          if arr currentPos  toString   equals item                mainCount    1                    countArray arr  currentPos 1  item

User · Answer

Here is my solution - The method takes an array of integers assuming the range between 0 to 100  as input and returns the number of occurrences of each element   let s say the input is  21 34 43 21 21 21 45 65 65 76 76 76   So the output would be in a map and it is   34 1  21 4  65 2  76 3  43 1  45 1     public Map lt Integer  Integer gt  countOccurrence int   numbersToProcess        int   possibleNumbers   new int 100       Map lt Integer  Integer gt  result   new HashMap lt Integer  Integer gt          for  int i   0  i  lt  numbersToProcess length    i          possibleNumbers numbersToProcess i     possibleNumbers numbersToProcess i     1        result put numbersToProcess i   possibleNumbers numbersToProcess i                return result

[java] Java count occurrence of each item in an array

Examples related to java

Examples related to arrays

Examples related to count