Sort array elements by frequency

Sorting array by using element frequency

Here given code implementation process.

//C++ Program 
//Sort array elements by frequency
#include <iostream>
#include <map> 
#include <vector>


using namespace std;

void occurrence(int arr[],int size)
{

  map<int, int> mp; 

  map <int , vector<int> > result;

  map<int, int> :: iterator element;

  map<int, vector<int>> :: iterator output;
  
  vector<int> :: iterator it;

  int j = size-1;

  

  //Find the frequency of array elements
  for (int i = 0; i < size; ++i)
  { 
    mp[arr[i]]++;
  }

  for (element = mp.begin(); element != mp.end(); ++element)
  {
    result[element->second].insert(result[element->second].begin(),element->first);
  }

  for (output = result.begin(); output != result.end(); ++output)
  {
    
    for(it = result[output->first].begin();it != result[output->first].end(); it++)
    {
      for(int i=0; i < output->first && j>=0;i++,j--)
      {
        //store the new result into array
        arr[j]=*it;
      }

    }
  }
  
    
}
void print_data(int arr[],int size)
{
  for (int i = 0; i < size; ++i)
  {
    cout<<arr[i]<<"  " ;
  }
  cout<<endl;
}
int main()
{
    //Array element
    int arr[] = {1, 3, 7, 4, 7, 4, 3,7, 4, 8, 7};
    //Get the size of array
    int size = sizeof(arr)/sizeof(arr[0]);
    print_data(arr,size);
    occurrence(arr,size);
    print_data(arr,size);
    return 0;
}

Output

  1  3  7  4  7  4  3  7  4  8  7
  7  7  7  7  4  4  4  3  3  1  8
/*
Java program
Sort array elements by frequency
*/
import java.util.*; 
public class Hashing 
{ 
  public static void occurrence(int []arr)
  {
    Map<Integer, Integer> map = new HashMap<>();
    Map<Integer, List<Integer>> result   = new HashMap<>();
    int j = arr.length-1;
    for (int i=0;i<arr.length ; i++ ) 
    {
      if (map.containsKey(arr[i])) 
      {  
        //when key exist then put new key
        map.put(arr[i],map.get(arr[i])+1);
      }
      else
      {
        map.put(arr[i],1);
      }
    }
    for(int key : map.keySet())
    {
      if (result.containsKey(map.get(key))) 
      { 
        result.get(map.get(key)).add(0,key);
      }
      else
      {
        // map.get(current_sum).add(i);
        result.put(map.get(key), new ArrayList<Integer> ());
        result.get(map.get(key)).add(0,key);
      }
    }
    for (int key : result.keySet()) 
    {
      for(int value: result.get(key))
      {

        for (int i=0;i<key && j >=0 ;i++,j-- ) 
        {
          arr[j]=value;
        }
      }
    }

  }
  public static void  print_data(int []arr)
  {
    int size=arr.length;
    for (int i = 0; i < size; ++i)
    {
      System.out.print(arr[i]+"  ") ;
    }
    System.out.println();
  }
  public static void main(String[] args) 
  {
    //Array element
    int []arr = {1, 3, 7, 4, 7, 4, 3,7, 4, 8, 7};
    print_data(arr);
    occurrence(arr);
    print_data(arr);
  }
}

Output

1  3  7  4  7  4  3  7  4  8  7  
7  7  7  7  4  4  4  3  3  1  8 
#Python program
#Sort array elements by frequency

class Hashing:

  def occurrence(self,listData):

    frequency={}
    output={}

    for key in listData:

      if key in frequency:
        frequency[key] += 1
      else:
        frequency[key] = 1
    

    for key, value in frequency.items():
      
      if value in output:
        output[value].insert(0,key)
      else:
         output[value] = [key]
   
    j=len(listData)-1
   
    for key, value in output.items():

      for element in value:
        i=0 
        while i<key and j >=0 :
          listData[j]=element
          i+=1
          j-=1


def main():
  obj = Hashing()
  #define list element
  item =[1, 3, 7, 4, 7, 4, 3,7, 4, 8, 7]
  print(item)
  obj.occurrence(item)
  print(item)

if __name__=="__main__":
  main()

Output

[1, 3, 7, 4, 7, 4, 3, 7, 4, 8, 7]
[7, 7, 7, 7, 4, 4, 4, 3, 3, 8, 1]
/*
C# program
Sort array elements by frequency
*/
using System;
using System.Collections.Generic;
public class Hashing 
{ 
  public static void occurrence(int []arr)
  {
    SortedDictionary<int,int> map = new SortedDictionary<int,int>();
    SortedDictionary<int,List<int>> result = new SortedDictionary<int,List<int>>();
    int j = arr.Length - 1;
    for (int i=0;i<arr.Length ; i++ ) 
    {
      if (map.ContainsKey(arr[i])) 
      {  
        //when key exist then put new key
        map[arr[i]]=map[arr[i]]+1;
      }
      else
      {
        map.Add(arr[i],1);
      }
    }
    foreach(KeyValuePair<int, int> entry in map)
    {
      
      if (result.ContainsKey(entry.Value)) 
      {  
        //when value exist then add new element in list
        result[entry.Value].Insert(0,entry.Key);
      }
      else
      {
        result[entry.Value]=new List<int>(){entry.Key};
      }
    }

    foreach(KeyValuePair<int, List<int>> entry in result)
    {
      
      for (int i = 0; i < (entry.Value).Count;i++ ) 
      {
        for (int k = 0; k <entry.Key ; k++,j--) 
        {
          arr[j]=entry.Value[i];
        }
      }

    }

  }
  public static void  print_data(int []arr)
  {
    int size=arr.Length;
    for (int i = 0; i < size; ++i)
    {
      Console.Write(arr[i]+"  ") ;
    }
    Console.WriteLine();
  }
  public static void Main(String[] args) 
  {
    //Array element
    int []arr = {1, 3, 7, 4, 7, 4, 3,7, 4, 8, 7};
    print_data (arr);
    occurrence(arr);
    print_data (arr);
  }
}

Output

1  3  7  4  7  4  3  7  4  8  7  
7  7  7  7  4  4  4  3  3  1  8 
<?php 
/*
* PHP Program 
Sort array elements by frequency
*/


class Hashing
{

  public function occurrence(&$arr)
  {
    $size= count($arr);

    $frequency=array();
    $output=array();
    for ($i=0; $i < $size ; ++$i) 
    { 
      if(array_key_exists($arr[$i],$frequency))
      {
        $frequency[$arr[$i]]= $frequency[$arr[$i]]+1;
      }
      else
      {
        $frequency[$arr[$i]]=1;
      }
      
    }
    ksort($frequency);
    foreach ($frequency as $key => $value) 
    {
      if(array_key_exists($value,$output))
      {
        array_unshift($output[$value],$key);
      }
      else
      {
        $output[$value]=array($key);
      }
    }
    $j=$size-1;
    ksort($output);

    foreach ($output as $key => $value) 
    {
      foreach ($value as $location => $data) 
      {
        for ($i=0; $i <$key && $j>=0 ; $i++,$j--) 
        { 
          $arr[$j]=$data;
        }
      }
    }
  }
  public function  print_data( $arr)
  {
    $size= count($arr);
    for ( $i = 0; $i < $size; ++$i)
    {
      echo $arr[$i]."  " ;
    }
    echo "\n";
  }

}


function main()
{
 $obj =new Hashing();
 $arr=array(1, 3, 7, 4, 7, 4, 3,7, 4, 8, 7);
 $obj->print_data($arr);
 $obj->occurrence($arr);
 $obj->print_data($arr);
}
main();
?>

Output

1  3  7  4  7  4  3  7  4  8  7  
7  7  7  7  4  4  4  3  3  1  8 


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