Retrieving different keys when the values in a hashmap are same???

[Kriss Tan]

Hi, would appreciate if anyone can help me out on this.

I have a series of keys and values that I would like to add into a hashmap.

I am printing out the order using the values, only one key will be selected although I have got 3 keys. I am sure that this is the problem of the same values in my Arraylist. Can anyone suggest a solution for this?

What i need is that if it had taken out the 1st key then it will move on to retrieve the 2nd key and so on even though the values are the same.


keys values
1 0.0
2 0.0
3 0.0

 

        List<Integer> mapKeys = new ArrayList<Integer>(rank.keySet());    //store all the keys listed above
        List<Double> mapValues = new ArrayList<Double>(rank.values());   //store all the values listed above
        List<Double> sortedMapValues = new ArrayList<Double>(rank.values());  //store all sorted values

          Collections.sort(sortedMapValues);
          System.out.println("Sorted Map Values" + sortedMapValues.toString());
          Object[] sortedArray = sortedMapValues.toArray();


 HashMap<Integer, Double> gMap = new LinkedHashMap<Integer, Double>();

     int size = sortedArray.length;

  for(int i=0; i<size; i++) {
                

            gMap.put(mapKeys.get(mapValues.indexOf(sortedArray[i])), sortedArray[i].toString());

           System.out.println("Order: " +gKeys.get(mapValues.indexOf(sortedArray[i])) + " " +sortedArray[i].toString());
           System.out.println("KEYS " +gMap.keySet());
        }

[Paul Clapham]

If you want the keys to be kept with the values, then don't write code which puts them in separate places and handles them separately. Something more like this:

Set<Map.Entry<Integer, Double>> entries = rank.entrySet();
List<Map.Entry<Integer, Double>> entryList = new ArrayList<Map.Entry<Integer, Double>>(entries);
Collections.sort(entryList, (a comparator which you write to compare your Map.Entry objects));
Map<Integer, Double> gMap = new LinkedHashMap<Integer, Double>();
for (Map.Entry<Integer, Double> entry: entryList) {
  gMap.put(entry.getKey(), entry.getValue();
}

As you see you still have to write a Comparator which orders Map.Entry<Integer, Double> objects via their Double value, but this is almost trivial.

[Kriss Tan]

Hi Paul, thanks for replying.

Is it possible for you to briefly explain the codes?

What is Map.Entry? etc.. I am still learning more about hashmap in the process..

Thanks!

[Paul Clapham]

Kriss Tan wrote:What is Map.Entry?

You'll find its API documentation here. And you'll find the API documentation for the java.util package, which contains all of the collections, here. Finally, you will find the Collections tutorial here.

Those should provide a much better learning tool than me trying to explain some specific code. Good luck!

[Kriss Tan]

Hey Paul,

I had spent some time reading through the API and tutorials but am unable to find a sample for comparing objects in Map.Entity.

Is it possible for you to provide me with some codes relating to comparing Map.Entity objects to work on with.

Thanks.

[Kriss Tan]

Hi Paul,

I revisit the codes and tried some sample codes and found out certain things I would like to clarify with you.

  
Set<Map.Entry<Integer, Double>> entries = rank.entrySet();   
List<Map.Entry<Integer, Double>> entryList = new ArrayList<Map.Entry<Integer, Double>>(entries);   
Collections.sort(entryList, (a comparator which you write to compare your Map.Entry objects));   
Map<Integer, Double> gMap = new LinkedHashMap<Integer, Double>();   
for (Map.Entry<Integer, Double> entry: entryList) {   
  gMap.put(entry.getKey(), entry.getValue();   
}  
  

Why do we need to create a Set Map.Entry object to store the rank. entry set?

I tried it by just storing it in the arrayList and it still works...Any reason why you particularly store it in a Set?

List<Map.Entry<Integer, Double>> entryList = new ArrayList<Map.Entry<Integer, Double>>(rank.entrySet();   
 

I changed to the above code written.

Looking forward to your reply.

Thanks!

[Paul Clapham]

That line of code is identical to the first two lines of code that I posted. The only difference is that my code assigns the entry set to a variable and then passes that variable to the ArrayList constructor, and yours passes the entry set directly to the ArrayList constructor. The end result is the same in both cases.

I did it that way because many people find it harder to understand complicated one-liners. Especially beginners.