How to sort Map?

[Chandra Bhatt]

Hi,

I have

Map<String,Long> amap = new HashMap<String,Long>();

I want to display the Map entries according to the Long values, corresponding
to the String, in the ascending order.

Please suggest, the proper way to do so!

Thanks,
cmbhatt
[ April 09, 2007: Message edited by: Chandra Bhatt ]

[Stuart Ash]

Sorry your question is not clear to me. Do you wish to sort based on keys or values?
If it's keys, it's quite simple, just use a TreeMap.

But it it's about sorting by the values, hmm...

[Stuart Ash]

... right, if you want to sort by values, consider a BidiMap implementation in the Apache Collections API:

Commons Collections

Cheers

[Chandra Bhatt]

Hey Stuart,

What if it is sort by values!

Stuart, you seem to me as fast as electricity. Before I could post, you had an
answer. Please suggest some conversion mechanism, converting values to list
and then sorting, then showing according to keys...

Isn't it?


Thanks,
cmbhatt
[ April 09, 2007: Message edited by: Chandra Bhatt ]

[Stuart Ash]

If you want to discuss the implementation of a new algorithm for this (instead of using the lovely apache commons code), you can rest assured I won't be as fast as electricity ..

let's see... can we use something other than a hashmap?

I can think of storing Map.Entry objects (if the HashMap object is already given to you, get the Entry object Set using the appropriate method)
in a List and sorting that list by using a custom Comparator which helps sort by Entry values.

Hope I am clear with the basic idea, but this is just a thought running in my head and I haven't considering all aspects of implementing it, but maybe you want to try some code taking this as a cue and we can discuss it further?

[saqib sarwar]

    
       Map<String,Long> amap = new HashMap<String,Long>();
       amap.put("a",new Long(423));
       amap.put("b",new Long(323));
       amap.put("c",new Long(411));
 
              
       Object []arr = amap.entrySet().toArray();
       
       Arrays.sort(arr,new Comparator(){
                                        public int compare(Object obj1,Object obj2){
                                                         Long lng1 =(Long)(((Map.Entry)obj1).getValue());
                                                         Long lng2 = (Long)(((Map.Entry)obj2).getValue());
                                                         return lng1.compareTo(lng2);
                                                         }
                                                      });
       for(Object a:arr)
           System.out.println(a.toString());

you might b looking for somthing like this.

[Chandra Bhatt]

Yeah Saqib,

That's true reply. That is what I was thinking of!

Thanks!


Regards,
cmbhatt

[saqib sarwar]

My Pleasur

[Stuart Ash]

The code posted by Saqib is not 100% Java5. Can you convert it to complete Java 5 (if you are taking the J5 exam)?

[Chandra Bhatt]

You are true Stuart,

Code compiles with warning!
I am trying to convert it to the form that compiles without warning(Java 5).

Thanks for reminding me!



Regards,
cmbhatt

[Bert Bates]

Also, let's make any Apache code "out of bounds" for a discussion in the SCJP forum :roll:

[Stuart Ash]

Originally posted by Bert Bates:
Also, let's make any Apache code "out of bounds" for a discussion in the SCJP forum :roll:

Why??

[Bert Bates]

The SCJP 5.0 exam already has a lot of topics! There's a lot of ground to cover, just to learn what's in the Sun objectives (which can be found here: http://www.sun.com/training/catalog/courses/CX-310-055.xml ).

In general, we like to reserve this forum for discussions that fall within the scope of topics that are covered in the exam. In this case, the relevent objective starts out:

"Use capabilities in the java.util package..."

Just trying to help everyone's studies be as efficient as possible

Thanks,

Bert

[Chandra Bhatt]

Hi Berts,

"Use capabilities in the java.util package..."

That is what my expectations were to have some solution straight from
java.util package. For current purpose (SCJP 5), people like me wont have
any interest to look forward for third party solutions.

My intention was to see how can we do that using java.util package.


Thanks,
cmbhatt

[Stuart Ash]

Thanks Bert for the explanation. Point taken. In fact, this dawned upon my mind (at least my subconscious mind!) after I asked the question here.

I agree -- and wholeheartedly, that the idea of this forum is to exercise one's own algorithmic skills within the bounds of the set objectives.

I was more in a developer mode than a certificate-aspirant one. I will recalibrate accordingly.

However, I reserve my old stand for just one reason: to those who may be willing to, poring over such pre-written code might give valuable ideas.

Of course, only Javafolk who have adequate experience in development would be amenable to doing this, and it seems to me that there are many here -- without being disparaging, who have less than a long-standing development experience. So, I guess I should mention such other pointers with the appropriate caveat!

[Bert Bates]

Thanks for your understanding Stuart! It IS an interesting topic and I think it would be fair if you wanted to spin off an Adobe thread, maybe in the Intermediate forum? I don't think this would qualify as a dreaded "cross-posting" In fact you could drop names if you want to, and if you do start another thread you could add the link to it here for those SCJP candidates who want to do a little "extra credit" studying

Bert

[Stuart Ash]

That seems to be a good way of doing it. I hope I don't find it too tedious to spawn another thread in an adjacent forum and the forum software we use makes it quite easy (lazy me )

Cheers.

[Arad Chear]

hi ,what about reverse the map then compare it as i see in K&B master exam (: