Best approach find position of an item in Lucene search results

Question

I am using Lucene.NET and able to search get hit results as ScoreDoc[].

I need to know specific item position in ScoreDoc[]. All items in ScoreDoc[] are unique.

Sample code: luceneSearcher.Search(query, collector); ScoreDoc[] scores = collector.TopDocs().scoreDocs

For example, I need to get find item position in ScoreDoc[], which has custom ID property where value could be '99999'.

I can iterate through item in scores[] and check for ID property which matches '99999' then return the position, but this can have performance hit because scores[] can have thousands of items.

Is there any better technique?

Thanks

Answer 1

I came up with creating new ExtendedCollector which stores CollectedDocuments.

    public class ExtendedCollector : Collector
    {
        private Scorer _scorer;
        private Int32 _docBase;
        private List<CollectedDocument> _documents;

        public ExtendedCollector()
        {
            _documents = new List<CollectedDocument>();
        }

        public override void SetScorer(Scorer scorer)
        {
            _scorer = scorer;
        }

        public override void Collect(int doc)
        {
            var docId = _docBase + doc;
            var score = _scorer.Score();

            var currentDoc = _documents.FirstOrDefault(d => d.DocId == docId);

            if (currentDoc == null)
                _documents.Add(new CollectedDocument()
                                   {DocId = docId, Score = score, OriginalIndex = _documents.Count, Index = _documents.Count});
            else
                currentDoc.Score = score;
        }

        public override void SetNextReader(IndexReader reader, int docBase)
        {
            _docBase = docBase;
        }

        public override bool AcceptsDocsOutOfOrder()
        {
            return false;
        }

        public List<CollectedDocument> Documents
        {
            get { return _documents; }
        }

        public List<CollectedDocument> DocumentsByScore
        {
            get
            {
                var result = _documents.OrderByDescending(d => d.Score).ToList();
                var itemId = 0;
                foreach (var collectedDocument in result)
                {
                    itemId++;
                    collectedDocument.Index = itemId;
                }

                return result;
            }
        }
    }

CollectedDocument looks like this

    public class CollectedDocument
    {
        public Int32 DocId { get; set; }
        public float Score { get; set; }
        public int OriginalIndex { get; set; }
        public int Index { get; set; }
    }

Whenever you want to get results you would do

        var myCollector = new ExtendedCollector();
        searcher.Search(searchQuery, myCollector);

        foreach (var doc in myCollector.Documents)
        {
            var docIndex = doc.Index; //this is the current index in a list
            var originalIndex = doc.OriginalIndex; //this is item Id set when doc was collected
        }

You can also get the documents ordered by score using

myCollector.DocumentsByScore

This might not be the easiest solution, but it works. If anyone has a better solution, please post it as I'd like to know that as well.