Sorting a HasMap by Values

[Abhik Ghosh]

I want to sort a HasMap by its values.

My code is :

  

import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

//sorting of data in a map by the values
public class MapSort 
{
	public static void main(String[] args) 
	{
		Map<Name,Val> m = new HashMap<Name,Val>();
		
		m.put(new Name("Angit"),new Val(10));
		m.put(new Name("Mohan"),new Val(89));
		m.put(new Name("Charu"),new Val(68));
		
		// now sort the map according to the value
		
		SortedMap s = new TreeMap(new MapComparator(m));
		
		
		Iterator iter = m.entrySet().iterator();
	    while(iter.hasNext())
	       System.out.println(iter.next());
	}
}


class Name
{
	String name;
	
	public Name(String str)
	{
		name = str;
	}
	
	public String getName()
	{
		return name;
	}
	
	//override equals
	public boolean equals(Object o)
	{
		return this.name.equals(((Name)o).getName());
	}
	
	
	//override hashCode
	public int hashCode()
	{
		return name.hashCode();
	}
}


class Val
{
	int marks;
	
	public Val(int marks)
	{
		this.marks = marks;
	}
	
	public int getMarks()
	{
		return marks;
	}
}

class MapComparator implements Comparator<Val>
{
	
	Map m;
	
	public MapComparator(Map m)
	{
		this.m = m;
	}
	
	public int compare(Val v1,Val v2)
	{
		if(v1.getMarks() == v2.getMarks())
			return 0;
		else if(v1.getMarks() > v2.getMarks())
			return 1;
		else
			return -1;
			
	}
}


  

But it is giving output as :
Name@3e0e7bf=Val@923e30
Name@4711993=Val@130c19b
Name@3c78865=Val@1f6a7b9

I want it to be sorted by the values.

Please help.

[Ankit Garg]

HashMap is not an ordered collection, you'll have to use an ordered collection like LinkedHashMap to be able to sort it. I'm quite sure there's nothing in the java API to sort it, you'll have to sort it manually, google is filled with solution for this - Link1, link2, link3, link4...

[Abhik Ghosh]

Thanks Ankit. That was a great help..

[S Ali]

  import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

//sorting of data in a map by the values
public class MapSort 
{
	public static void main(String[] args) 
	{
		Map<Name,Val> m = new HashMap<Name,Val>();
		
		m.put(new Name("Angit"),new Val(10));
		m.put(new Name("Mohan"),new Val(89));
		m.put(new Name("Charu"),new Val(68));
				
		// now sort the map according to the value
		
		
		SortedMap s = new TreeMap(new MapComparator(m));
		s.putAll(m);
		
		Iterator iter = m.entrySet().iterator();
	    while(iter.hasNext())
	       System.out.println(iter.next());
	    
	    System.out.println(s);
	}
}


class Name
{
	String name;
	
	public Name(String str)
	{
		name = str;
	}
	
	public String getName()
	{
		return name;
	}
	
	//override equals
	public boolean equals(Object o)
	{
		return this.name.equals(((Name)o).getName());
	}
	
	
	//override hashCode
	public int hashCode()
	{
		return name.hashCode();
	}
	public String toString()
	{
		return name;
	}
}


class Val
{
	int marks;
	
	public Val(int marks)
	{
		this.marks = marks;
	}
	
	public int getMarks()
	{
		return marks;
	}
	
	public String toString()
	{
		return marks+ "";
	}
}

class MapComparator implements Comparator<Name>
{
	
	Map<Name,Val> m;
	
	public MapComparator(Map <Name,Val>m)
	{
		this.m = m;
	}
	
	public int compare(Name v1,Name v2)
	{
		if(m.get(v1).getMarks()== m.get(v2).getMarks())
			return 0;
		else if(m.get(v1).getMarks() > m.get(v2).getMarks())
			return 1;
		else
			return -1;
		

			
	}
}


    

1- first you defined your Treemap but you didn't put entries of Hashmap in it.
s.putAll(m);

2- second in your comparator you should have compared the map's values getting them thought your key so it can iterate on all values of the map.

The code now prints:
Charu=68
Mohan=89
Angit=10
{Angit=10, Charu=68, Mohan=89} -----> after sorting

[Abhik Ghosh]

Thanks Ali. I have also just written a fresh code that sorts a HashMap both by keys as well as by values.
Here it is:

  

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

public class MapSort 
{
	public static void main(String[] args) 
	{
		Map<Integer,String> m = new LinkedHashMap<Integer, String>();
		
		m.put(1,"vsklv");
		m.put(100,"xvc");
		m.put(32,"sswweds");
		
		//sort by key
		
		Object[] keyarr = m.keySet().toArray();
		
		Arrays.sort(keyarr);
		
		//put the values in the map
		
		Map<Integer,String> m2 = new LinkedHashMap<Integer, String>();
		
		for (int i = 0; i < keyarr.length; i++)
		{
			m2.put((Integer) keyarr[i],m.get(keyarr[i]));
		}
		
		Iterator it = m2.entrySet().iterator();
		while(it.hasNext())
			System.out.println(it.next());
		
				
		
		
		//sort by value
		
		List<Integer> ls1 = new ArrayList<Integer>(m.keySet());
		List<String> ls2 = new ArrayList<String>(m.values());
		
		Object[] valarr = m.values().toArray();
		
		Arrays.sort(valarr);
		
		//put the values in the map
		
		Map<Integer,String> m3 = new LinkedHashMap<Integer, String>();
		
		for (int i = 0; i < valarr.length; i++)
		{
			m3.put(ls1.get(ls2.indexOf(valarr[i])),(String)valarr[i]);
		}
		
		
		Iterator iter = m3.entrySet().iterator();
		while(iter.hasNext())
			System.out.println(iter.next());
		
	}
}

[Abhik Ghosh]

And Ali.. thanks a lot for correcting my code.

[S Ali]

No problem bro

[Deepak Bala]

To add to your discussion, it is very unlikely that a hashmap would need to be sorted by its values. If there is a requirement that dictates that this should happen, you should look at your problem and data structure selection again.