Sorting a Hashmap according to values

06 Apr, 2022
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 valuesimport 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());        }    }}
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 valuesimport 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());        }    }}
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 Streams in Java 8
Here we will use streams to sort the map. We will use the stream() method to get the stream of entrySet followed by the lambda expression inside sorted() method to sort the stream and finally, we will convert it into a map using toMap() method. Inside the toMap() method, we use the LinkedHashMap::new method reference to retain the sorted order of the map.
Java
// Java program to sort hashmap by valuesimport static java.util.stream.Collectors.*; import java.lang.*;import java.util.*;import java.util.stream.*;import java.util.stream.Collectors;public class gfg3 {     // function to sort hashmap by values    public static HashMap<String, Integer>    sortByValue(HashMap<String, Integer> hm)    {        HashMap<String, Integer> temp            = hm.entrySet()                  .stream()                  .sorted((i1, i2)                              -> i1.getValue().compareTo(                                  i2.getValue()))                  .collect(Collectors.toMap(                      Map.Entry::getKey,                      Map.Entry::getValue,                      (e1, e2) -> e1, LinkedHashMap::new));         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());        }    }}
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
rajatagrawal5
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