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From "Mike O'Leary" <tmole...@uw.edu>
Subject RE: Problem with TermVector offsets and positions not being preserved
Date Wed, 22 Aug 2012 21:23:26 GMT
I have one more question about term vector positions and offsets being preserved. My co-worker
is working on updating the documents in an index with a field that contains a numerical value
derived from the term frequencies and inverse document frequencies of terms in the document.
His first pass at doing this calculates these values, writes them along with document ids
to a text file and then updates the documents by reading lines from the file, searching for
the document that contains the id, adding the field to the document, and replacing the document
in the index. Some of the fields in these documents have term vectors with offsets and positions.
After the revised document is updated in the index, those fields' term vector offsets and
positions are still found. After closing the searcher, reader and writer that are used in
this process, the fields that have term vectors no longer have positions and offsets in them.
His code looks like this:

IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_36, _analyzer);
IndexWriter writer = new IndexWriter(indexDir, config);
IndexReader reader = IndexReader.open(writer, true);
IndexSearcher searcher = new IndexSearcher(reader);

while ((s = in.readLine()) != null) {
    String[] tokens = s.split(",");
    float fieldValue = Float.parseFloat(tokens[1].trim());
    NumericField nField = new NumericField("freqVal", Field.Store.YES, true);
    nField.setFloatValue(fieldValue);
    String docId = tokens[0].trim();
    Term docIdTerm = new Term("DocId", docId);
    TermQuery query = new TermQuery(docIdTerm);
    TopDocs hits = searcher.search(query, 2);
  
    if (hits.scoreDocs.length != 1) {
        throw new Exception("Unexpected number of documents in index with docId = " + docId);
    }
    int docNum = hits.scoreDocs[0].doc;
    Document doc = searcher.doc(docNum);
    doc.add(nField);
    writer.updateDocument(docIdTerm, doc);
}
displayTermVectorInfo(dir);   // for debugging
writer.close();
displayTermVectorInfo(dir);   // for debugging
reader.close();
searcher.close();

private static void displayTermVectorInfo(Directory dir) throws IOException, CorruptIndexException
{
    IndexReader reader = null;

    try {
        reader = IndexReader.open(dir);

        for (int i = 0; i < reader.numDocs; i++) {
            Document doc = reader.document(j);
            List<Fieldable> docFields = doc.getFields();

            for (Fieldable field : docFields) {
                TermFreqVector termFreqVector = reader.getTermFreqVector(i, field.name());
      
                if (termFreqVector != null && termFreqVector instanceof TermPositionVector)
{
                    TermPositionVector termPositionVector = (TermPositionVector)termFreqVector;
                    System.out.println("Field " + field.name());

                    for (int j = 0; j < termFreqVector.size(); j++) {
                        TermVectorOffsetInfo[] offsets = termPositionVector.getOffsets(j);
                        
                        for (TermVectorOffsetInfo offsetInfo : offsets) {
                            System.out.println("offset: " + offsetInfo.getStartOffset() +
" " + offsetInfo.getEndOffset());
                        }
                    }
                    for (int k = 0; k < termFreqVector.size(); k++) {
                        int[] positions = termPositionVector.getTermPositions(k);

                        for (int position : positions) {
                            System.out.println("position: " + position);
                        }
                    }
                }
            }
        }
    } finally {
        if (reader != null) {
            reader.close();
        }
    }
}

The first time displayTermVectorInfo is called, it displays offsets and positions for the
fields that have term vectors with offsets and positions. The second time it is called, it
doesn't display anything because none of the term vectors satisfy termFreqVector instanceof
TermPositionVector. Is it supposed to work this way? What is it about closing the writer that
alters the term vectors in the affected fields? Is there a way to add a field to the documents
in an index in which this doesn't occur?
Thanks,
Mike


-----Original Message-----
From: Robert Muir [mailto:rcmuir@gmail.com] 
Sent: Friday, July 20, 2012 5:59 PM
To: java-user@lucene.apache.org
Subject: Re: Problem with TermVector offsets and positions not being preserved

On Fri, Jul 20, 2012 at 8:24 PM, Mike O'Leary <tmoleary@uw.edu> wrote:
> Hi Robert,
> I'm not trying to determine whether a document has term vectors, I'm trying to determine
whether the term vectors that are in the index have offsets and positions > stored.

Right: what i'm trying to tell you is that offsets and positions is not an index-wide setting
for a field: its per-document.

I think all the tools you are using to check these values are not doing it correctly:
1. DumpIndex is wrongly using values from the Document returned by IndexReader.document(),
but that doesn't and never did retrieve these values (it would be 2 extra disk seeks per document
to figure out the term vector flags) 2. I havent looked at Luke, but its probably printing
the "global"
bits from FieldInfos. It used to be that we wrote some bits for these options, I don't ever
know what the purpose was since these options can be controlled on/off at a per-document level:
they make no sense.
Because of this we stopped writing these bits in 3.6 (we only write into FieldInfos if the
field has any term vectors at all), and thats probably whats confusing you there.

Again, if you really want to validate that a specific document has offsets/positions in its
term vectors, you need to check that specific document with IndexReader.getTermFreqVector,
there is no other way, since this can be controlled on a per-document basis for a field.


--
lucidimagination.com

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