How to sort values in hashmap by using treeset?

Question

I have keys values, now I would like sort values only by adding it to the tree-set. Because tree-set performs the ascending order sorting.

There exist a method that converting called converting map to list. But it is a hectic method, can any one comment about this?

package practice;
import java.io.ObjectInputStream.GetField;
import java.util.*;
import java.util.Map.Entry;

public class example1{
    public static void main(String[] args) {
        Map<Integer,String> map = new HashMap<Integer,String>();
        map.put(1, "h");
        map.put(2, "l");
        map.put(3, "a");
        System.out.println(map);
        System.out.println("unsort");
        for(Map.Entry m:map.entrySet()) {
            System.out.println(m.getKey()+" - "+m.getValue());
        }
        System.out.println("sorting by values");
    }
}

Please provide the code you are working with so we can see the issue in action. — RedBassett, Feb 06 '17 at 10:41
You can use the "edit" button below your question to add this to the original question! — RedBassett, Feb 06 '17 at 10:56
here are a few options: http://stackoverflow.com/questions/109383/sort-a-mapkey-value-by-values-java — Andreas, Feb 06 '17 at 19:36

score 1 · Answer 1 · answered Feb 06 '17 at 10:51

1

Yes you can do this:

HashMap<String, String> hashmap = new HashMap<>();
hashmap.put("k1", "Zz");
hashmap.put("k2", "A");
hashmap.put("k3", "Zd");
hashmap.put("k4", "Zd");

TreeSet<String> set = new TreeSet<>(hashmap.values());

But be careful, in this example this way of "sorting" wil result in a set containing 3 elements (the 4th "k4" entry in hashmap will get lost)

I would recommend to use java streams

List<String> collect = hashmap.values().stream().sorted().collect(Collectors.toList());

this will sort and keep all values.

answered Feb 06 '17 at 10:51

kamehl23

522
3
6

List collect = hashmap.values().stream().sorted().collect(Collectors.toList()); what is this?? – Attri Feb 06 '17 at 11:03
1

"Stream is a new abstract layer introduced in Java 8. Using stream, you can process data in a declarative way similar to SQL statements" -> see https://www.tutorialspoint.com/java8/java8_streams.htm – kamehl23 Feb 06 '17 at 11:14

score 1 · Answer 2 · answered Jul 10 '19 at 06:15

    String s1 = new String("A");
    String s2 = new String("B");
    String s3 = new String("C");
    String s4 = new String("D");
    String s5 = new String("F");

    Map<String,String> map1 = new HashMap<>();

    map1.put(s1, "AAA");
    map1.put(s2, "BBB");
    map1.put(s3, "CCC");
    map1.put(s4, "FFF");
    map1.put(s5, "DDD");

    System.out.println(map1);


    Set<Map.Entry<String, String>> set = new TreeSet<>(new SortHashValue());
    set.addAll(map1.entrySet());
    System.out.println(set);

   class SortHashValue implements Comparator<Map.Entry<String, String>>{
   public int compare(Entry<String, String> e1, Entry<String, String> e2) {
    String v1 = e1.getValue();
    String v2 = e2.getValue();
    return v1.compareTo(v2);
}
}

Thank you for this code snippet, which might provide some limited, immediate help. A [proper explanation](https://meta.stackexchange.com/q/114762/349538) would greatly improve its long-term value by showing why this is a good solution to the problem and would make it more useful to future readers with other, similar questions. Please [edit] your answer to add some explanation, including the assumptions you’ve made. — Dwhitz, Jul 10 '19 at 06:39

How to sort values in hashmap by using treeset?

2 Answers2