Sorting a Hashmap according to values

Software Development
#1

Hello Everyone,

Given marks scored out of 100 by a student in subjects where the 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 the list and put them in a new hashmap. Thus, a new hashmap is sorted according to values.
Below is the implementation of the above idea:

  • Java

// 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

Using Java 8 Lambdas

Here we will change how we did sorting and will use lambda expression for sorting. The logic is the same, and even we also passed the comparator object but only using lambda.

Below is the implementation of the above approach:

  • Java

// Java program to sort hashmap by values

import java.lang.*;

import java.util.*;

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 using lambda expression

Collections.sort(

list,

(i1,

i2) -> i1.getValue().compareTo(i2.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