Java: sort ids by score

Question

I have a set of objects, each of which has an id value (int). I want to write a function which takes the object set as input, calculates a score (double) for each object, and returns a sorted array of object ids where the returned ids are stored in order of the "score" obtained.

I thought this would be easy, but I can't find a simple way of achieving this in less than 10 lines of code. (I'm using jdk 7)

Here's my code:

private ArrayList<Integer> getBlockIds(IndexKey key) {
    ArrayList<Integer> blockIds;
    Set<IndexKey> adjKeys = indexAPI.getAdjacentKeys(key, 1);
    Comparator cmp = new Comparator("Levenshtein"); 
    for ( IndexKey aKey : adjKeys ) {
        if ( cmp.similarity(key.getValue(), aKey.getValue()) >= 0.75 ) { 
            blockIds.add(aKey.getBlockId);
        }
    }
    return blockIds;
}

I want blockIds to be stored in order of score (highest first)

http://stackoverflow.com/questions/109383/how-to-sort-a-mapkey-value-on-the-values-in-java/1283722#1283722 - but I thought there must be a simpler way than this if I'm just dealing with numerical values — swami, Mar 16 '15 at 09:44
no reason for 10 lines per se... just thought there should be a very simple way of doing this — swami, Mar 16 '15 at 09:45
Well, I'd write a `Comparator`, and use some kind of `SortedSet` such as a `TreeSet`. I don't think I could make it fit in 10 lines. — Dawood ibn Kareem, Mar 16 '15 at 09:47
@David The scores are not attributes of the input Objects, they are calculated for each object in relation to another object. Have updated the question so it's clearer. — swami, Mar 16 '15 at 09:57
Doesn't matter. The `Comparator` can still call the method that calculates the score. — Dawood ibn Kareem, Mar 16 '15 at 09:58

Bohemian · Answer 1 · 2015-03-16T09:58:53.587

1

You only need one line actually.

Given:

Set<MyClass> set;

And methods int getId() and int getScore():

List<MyClass> sorted = set.stream().sort((a, b) -> a.getScore() - b.getScore()).map(MyClass::getId).collect(Collectors.toList());

edited Mar 16 '15 at 09:58

answered Mar 16 '15 at 09:54

Bohemian

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Looks like Java 8 code... I'm using 7 - have updated my question so its clear. – swami Mar 16 '15 at 09:59
@swami java 8 has been out for a year now. Just curious, why can't you use it? – Bohemian Mar 16 '15 at 10:00

score 0 · Answer 2 · answered Mar 16 '15 at 10:42

Here's what I came up with, based on David's suggestion

private TreeSet<Integer> getBlockIds(IndexKey key) {
    StringDistance sd = new StringDistance("Levenshtein"); //take from config
    TreeSet<IndexKey> orderedKeys = new TreeSet<IndexKey>(new Comparator<IndexKey>() {
        @Override
        private int compare(IndexKey k1, IndexKey k2) {
            double k1Score = sd.similarity(key.getValue(), k1.getValue());
            double k2Score = sd.similarity(key.getValue(), k2.getValue());
            return k1Score.compareTo(k2Score);
        }
    });
    Set<IndexKey> adjKeys = indexAPI.getAdjacentKeys(key, 1);
    for ( IndexKey aKey : adjKeys ) {
        if ( sd.similarity(key.getValue(), aKey.getValue()) >= 0.75 ) { //take from config
            orderedKeys.add(aKey);
        }
    }
    TreeSet<Integer> blockIds;
    for ( IndexKey k : orderedKeys ) {
        blockIds.add(k.getBlockId);
    }
    return blockIds;
}

Java: sort ids by score

2 Answers2