Question

I am looking for a way to find the terms that matched in the document using waldcard search in Lucene. I used the explainer to try and find the terms but this failed. A portion of the relevant code is below.

ScoreDoc[] myHits = myTopDocs.scoreDocs;
int hitsCount = myHits.Length;
for (int myCounter = 0; myCounter < hitsCount; myCounter++)
{
    Document doc = searcher.Doc(myHits[myCounter].doc);
    Explanation explanation = searcher.Explain(myQuery, myCounter);
    string myExplanation = explanation.ToString();
    ...

When I do a search on say micro*, documents are found and it enter the loop but myExplanation contains NON-MATCH and no other information.

How do I get the term that was found in this document ?

Any help would be most appreciated.

Regards

Answer 1

    class TVM : TermVectorMapper
    {
        public List<string> FoundTerms = new List<string>();
        HashSet<string> _termTexts = new HashSet<string>();

        public TVM(Query q, IndexReader r) : base()
        {
            List<Term> allTerms = new List<Term>();
            q.Rewrite(r).ExtractTerms(allTerms);
            foreach (Term t in allTerms) _termTexts.Add(t.Text());
        }

        public override void SetExpectations(string field, int numTerms, bool storeOffsets, bool storePositions)
        {
        }

        public override void Map(string term, int frequency, TermVectorOffsetInfo[] offsets, int[] positions)
        {
            if (_termTexts.Contains(term)) FoundTerms.Add(term);
        }
    }

    void TermVectorMapperTest()
    {
        RAMDirectory dir = new RAMDirectory();
        IndexWriter writer = new IndexWriter(dir, new Lucene.Net.Analysis.Standard.StandardAnalyzer(), true);
        Document d = null;

        d = new Document();
        d.Add(new Field("text", "microscope aaa", Field.Store.YES, Field.Index.ANALYZED,Field.TermVector.WITH_POSITIONS_OFFSETS));
        writer.AddDocument(d);

        d = new Document();
        d.Add(new Field("text", "microsoft bbb", Field.Store.YES, Field.Index.ANALYZED, Field.TermVector.WITH_POSITIONS_OFFSETS));
        writer.AddDocument(d);

        writer.Close();

        IndexReader reader = IndexReader.Open(dir);
        IndexSearcher searcher = new IndexSearcher(reader);

        QueryParser queryParser = new QueryParser("text", new Lucene.Net.Analysis.Standard.StandardAnalyzer());
        queryParser.SetMultiTermRewriteMethod(MultiTermQuery.SCORING_BOOLEAN_QUERY_REWRITE); 
        Query query = queryParser.Parse("micro*");

        TopDocs results = searcher.Search(query, 5);
        System.Diagnostics.Debug.Assert(results.TotalHits == 2);

        TVM tvm = new TVM(query, reader);
        for (int i = 0; i < results.ScoreDocs.Length; i++)
        {
            Console.Write("DOCID:" + results.ScoreDocs[i].Doc + " > ");
            reader.GetTermFreqVector(results.ScoreDocs[i].Doc, "text", tvm);
            foreach (string term in tvm.FoundTerms) Console.Write(term + " ");
            tvm.FoundTerms.Clear();
            Console.WriteLine();
        }
    }