Sorting a Hashmap according to values

Difficulty Level : Hard
Last Updated : 11 Dec, 2018

Given marks scored out of 100 by a student in subjects where name of the subject is key and marks scored is the value. Our task is to sort the hashmap according to values i.e. according to marks.

Example:

Input : Key = Math, Value = 98
        Key = Data Structure, Value = 85
        Key = Database, Value = 91
        Key = Java, Value = 95
        Key = Operating System, Value = 79
        Key = Networking, Value = 80

Output : Key = Operating System, Value = 79
         Key = Networking, Value = 80
         Key = Data Structure, Value = 85
         Key = Database, Value = 91
         Key = Java, Value = 95
         Key = Math, Value = 98

Solution: The idea is to store the entry set in a list and sort the list on the basis of values. Then fetch values and keys from list and put them in new hashmap. Thus new hashmap is sorted according to values.

Below is implementation of the above idea:

// Java program to sort hashmap by values 
import java.util.*; 
import java.lang.*; 
  
public class GFG { 
  
    // function to sort hashmap by values 
    public static HashMap<String, Integer> sortByValue(HashMap<String, Integer> hm) 
    { 
        // Create a list from elements of HashMap 
        List<Map.Entry<String, Integer> > list = 
               new LinkedList<Map.Entry<String, Integer> >(hm.entrySet()); 
  
        // Sort the list 
        Collections.sort(list, new Comparator<Map.Entry<String, Integer> >() { 
            public int compare(Map.Entry<String, Integer> o1,  
                               Map.Entry<String, Integer> o2) 
            { 
                return (o1.getValue()).compareTo(o2.getValue()); 
            } 
        }); 
          
        // put data from sorted list to hashmap  
        HashMap<String, Integer> temp = new LinkedHashMap<String, Integer>(); 
        for (Map.Entry<String, Integer> aa : list) { 
            temp.put(aa.getKey(), aa.getValue()); 
        } 
        return temp; 
    } 
  
    // Driver Code 
    public static void main(String[] args) 
    { 
  
        HashMap<String, Integer> hm = new HashMap<String, Integer>(); 
  
        // enter data into hashmap 
        hm.put("Math", 98); 
        hm.put("Data Structure", 85); 
        hm.put("Database", 91); 
        hm.put("Java", 95); 
        hm.put("Operating System", 79); 
        hm.put("Networking", 80); 
        Map<String, Integer> hm1 = sortByValue(hm); 
  
        // print the sorted hashmap 
        for (Map.Entry<String, Integer> en : hm1.entrySet()) { 
            System.out.println("Key = " + en.getKey() +  
                          ", Value = " + en.getValue()); 
        } 
    } 
} 

Output:

Key = Operating System, Value = 79
Key = Networking, Value = 80
Key = Data Structure, Value = 85
Key = Database, Value = 91
Key = Java, Value = 95
Key = Math, Value = 98

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