Question

I would like to know a way to implement a scenario that I am trying to do.

I have a HashSet of Objects with Object having an attribute A of type int. Now, I want a representative from each of the distinct partitions of HashSet based on the distinct values of the attribute A.

For example:
Let the HashSet be

{O1, O2, O3, O4, O5, O6} where O1 to O6 are objects with attribute values as follows

Partition #1
O1.A = 1
O2.A = 1
Partition #2
O3.A = 2
O4.A = 2
O5.A = 2
Partition #3
O6.A = 3

I want a representative from each partition,

e.g. {O1, O4, O6} 

Can anybody suggest some way to do this? Any help will be appreciated.

Thanks,

Somnath

Answer 1

Make a Map<Integer, YourClass> (probably best a TreeMap, so the partitions are in order), and copy the data into it:

 Map<Integer, YourClass> partitions = new TreeMap<Integer, YourClass>();
 for (YourClass x: set){
    Integer p = x.getA();
    if (partitions.containsKey(p))
       continue;
    partitions.put(p, x);
 }

After this, partitions contains one entry for every partition found, with one representative each (the first one found).

Set<YourClass> representatives = partitions.values();