Question

This code takes 9 minutes to run for a set of 5,600 objects:

public Set<UnDirectedPair<T>> getAllUndirectedPairs(Set<T> setObjects) {
    Set<T> setObjectsProcessed = new TreeSet();
    Set<UnDirectedPair<T>> setPairs;
    setPairs = new TreeSet();
    Iterator<T> setObjectsIteratorA = setObjects.iterator();
    Iterator<T> setObjectsIteratorB;
    T currTA;
    T currTB;
    while (setObjectsIteratorA.hasNext()) {
        currTA = setObjectsIteratorA.next();
        setObjectsProcessed.add(currTA);
        setObjectsIteratorB = setObjects.iterator();
        while (setObjectsIteratorB.hasNext()) {
            currTB = setObjectsIteratorB.next();
            if (!setObjectsProcessed.contains(currTB) && !currTA.equals(currTB)) {
                setPairs.add(new UnDirectedPair(currTA, currTB));
            }
        }
        setObjectsProcessed.add(currTA);
    }
    return setPairs;

}

Looking for a way to dramatically reduce the running time… ideas?

[BACKGROUND]
The set contains Persons. There are duplicates in the set (same persons, but with slightly different attributes because errors at input time). I have methods which take 2 Persons and make the necessary corrections. So, as a preliminary step, I need to create a Set of Pairs of (Person, Person) which will be fed to these methods.

Answer 1

Thanks for good suggestions.

The basic impairment was my class UnDirectedPair which had expensive equals and compareTo methods. I replaced it with a stripped bare Pair class.
This got the code to run in approx 10s.

Still, using operations on sets seemed costly. With @mawia suggestion modified a bit, sets can be left completely out of the picture. The final code runs in under 2 seconds instead of 9mn 40s – returning a list of 19,471,920 Pair objects!!

public List<Pair<T>> getAllUndirectedPairsAsList(Set<T> setObjects) {
    List<T> listObjects = new ArrayList();
    listObjects.addAll(setObjects);

    List<Pair<T>> listPairs = new ArrayList();
    Iterator<T> listIterator1 = listObjects.listIterator();
    Iterator<T> listIterator2;
    int count = 1;
    T object1;
    while (listIterator1.hasNext()) {
        object1 = listIterator1.next();
        listIterator2 = listObjects.listIterator(count++);
        while (listIterator2.hasNext()) {
            listPairs.add(new Pair(object1, listIterator2.next()));
        }
    }
    return listPairs;
}