CODEWITHSUNDEEP
javasortingdictionary
Dilip
Dilip

Reputation: 959

Sort a Map in Java is not working

I am trying to sort a TreeMap (having Double as a value and Integer value as a key) using Comparator interface but it's not working.

// Create a tree map
        TreeMap tm = new TreeMap();
        // Put elements to the map
        tm.put(1, new Double(3434.34));
        tm.put(0, new Double(123.22));
        tm.put(4, new Double(1378.00));
        tm.put(2, new Double(99.22));
        tm.put(3, new Double(-19.08));
        List<Map.Entry> valueList = new ArrayList(tm.entrySet());

        // Collections.sort(valueList, new Sort());

        Collections.sort(valueList, new Sort());

        HashMap sortedMap = new HashMap();

        // Get an iterator
        Iterator<Map.Entry> i = valueList.iterator();

        // Display elements
        while (i.hasNext()) {
            Map.Entry object = i.next();
            sortedMap.put(object.getKey(), object.getValue());
        }
        List sortedList = new ArrayList(sortedMap.entrySet());
        Iterator<Map.Entry> iterator = sortedList.iterator();
        while (iterator.hasNext()) {
            Map.Entry entry = iterator.next();
            System.out.println("Value " + entry.getValue() + "\n");
        }

The following is my Comparator class

public class Sort implements Comparator<Map.Entry> {

    @Override
    public int compare(Map.Entry o1, Map.Entry o2) {
        // TODO Auto-generated method stub
        double valueOne = (Double) o1.getValue();
        double valueTwo = (Double) o2.getValue();

        int returnValue =
            valueOne > valueTwo ? -1 : (valueOne == valueTwo ? 0 : 1);

        return (valueOne > valueTwo ? -1 : (valueOne == valueTwo ? 0 : 1));
    }

}

But i am getting the following output

Value 123.22

Value 3434.34

Value 99.22

Value -19.08

Value 1378.0

Edited Part

public int compare(Map.Entry o1, Map.Entry o2) {
        // TODO Auto-generated method stub
        double valueOne = ((Double) o1.getValue()).doubleValue();
        double valueTwo = ((Double) o2.getValue()).doubleValue();

        int returnValue =
            valueOne > valueTwo ? -1 : (valueOne == valueTwo ? 0 : 1);

        return (valueOne > valueTwo ? -1 : (valueOne == valueTwo ? 0 : 1));
    }

Upvotes: 2

Views: 334

Answers (5)

yshavit
yshavit

Reputation: 43456

The Comparator works only your keys, not entries. You need a Comparator<Integer>, and pass in instance of this Comparator to the TreeMap constructor.

TreeMap<Integer,Double> tm = new TreeMap<Integer,Double>(myIntegerComparator);

In your example, the behavior you see is due to the TreeMap using Integer's standard comparsion (this works because Integer is Comparable<Integer>).

(Btw, you should also read up on generics and use them in your collections classes, as well as any other parameterized class.)

Upvotes: 1

Bitmap
Bitmap

Reputation: 12538

Adding to what others have already suggested, try this:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

public class SortDemo
{
  public class Sort implements Comparator<Map.Entry>
  {
    public int compare(Entry o1, Entry o2)
    {
      Double valueOne = (Double) o1.getValue();
      Double valueTwo = (Double) o2.getValue();
      return (int) Math.signum(valueOne.compareTo(valueTwo));
    }
  }

  public static void main(String[] args)
  {
    new SortDemo().foo();
  }

  void foo()
  {
    TreeMap tm = new TreeMap();
    tm.put(1, new Double(3434.34));
    tm.put(0, new Double(123.22));
    tm.put(4, new Double(1378.00));
    tm.put(2, new Double(99.22));
    tm.put(3, new Double(-19.08));

    List<Map.Entry> valueList = new ArrayList(tm.entrySet());
    Collections.sort(valueList, new Sort());

    Iterator<Map.Entry> iterator = valueList.iterator();
    while (iterator.hasNext())
    {
      Map.Entry entry = iterator.next();
      System.out.println("Value: " + entry.getValue());
    }
  }
}

Upvotes: 1

eabraham
eabraham

Reputation: 4164

Using a HashMap for sorting will not work because its not a list. You need to look into an ArrayList and the sort method.

ArrayList<double> arr = new ArrayList<double>();
sort(arr) //sort ascending

Upvotes: 0

GriffeyDog
GriffeyDog

Reputation: 8386

When you put them into the HashMap they will not retain their order, as a HashMap is not an ordered map.

Upvotes: 1

SLaks
SLaks

Reputation: 888213

HashMap is intrinsically unordered.

Instead, you can create a TreeMap with your comparator in the first place.

Upvotes: 5

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