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From Joshua O'Madadhain <jmad...@ics.uci.edu>
Subject number of terms vs. number of fields
Date Sun, 02 Dec 2001 02:55:21 GMT
I have been experimenting with indexing a document set with different sets
of fields.  Specifically, I start out with a "contents" field that
is a concatenation of all the elements of the original document in which
I'm interested.  This gets me an index with about 7500 unique terms (which
I determine by opening up an IndexReader, extracting the terms in the
index, and counting them).  Then I've been adding each of the separate
elements (title, major subject, minor subject, abstract/extract), one at a
time, to the index (by recreating the index).  

Because "contents" is the concatenation of the other fields ("title",
"major", "minor", "abstract"/"extract"), I would expect that the number of
unique terms in the index would not change if I added the other fields
into the index; each term should just have twice the frequency
as if I only used the "contents" field.  However, this is not what's
happening; in fact, if I add all the other fields in, the total number of
unique terms is 22000+.

I have verified that "contents" contains everything that the other fields
do, so I am quite puzzled by this.  Any idea what's going on here, and
why?

For anyone who might be interested in checking this out, my code is below.

Regards,

Joshua


// FileCFDocument.java (a modified version of FileDocument.java in the
// source examples)
import java.io.File;
import java.io.FileInputStream;
import java.util.Vector;

import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;

/** A utility for making Lucene Documents from a File. */

public class FileCFDocument
{
    public static Document[] makeDocuments(File f)
        throws java.io.FileNotFoundException, java.io.IOException
    {
        // open file, read it into a byte array and thence a String
        FileInputStream fis = new FileInputStream(f);
        int n = fis.available();
        byte[] data = new byte[n];
        fis.read(data);
        fis.close();

        String s = new String(data);
        int ti, so, mj, mn, ab, ex, rf, abex;

        Vector vdocs = new Vector();
        String contents;

        // fields being indexed:
        // TI (title)
        // MJ (major subject)
        // MN (minor subject)
        // AB/EX (abstract/extract)

        ti = s.indexOf("\nTI ");
        while (ti != -1)
        {
            // make a new, empty document
            Document doc = new Document();

            int k = s.indexOf("\nPN ");
            doc.add(Field.UnIndexed("number", s.substring(k+4, k+9)));

            // DEBUG
            System.out.println(s.substring(k, k+9));

            s = s.substring(ti+4);

            // DEBUG
            System.out.println("s.length(): " + s.length());

            so = s.indexOf("\nSO ");
            mj = s.indexOf("\nMJ ");
            mn = s.indexOf("\nMN ");
            ab = s.indexOf("\nAB ");
            ex = s.indexOf("\nEX ");
            rf = s.indexOf("\nRF ");

//            System.out.println("so: " + so + ", mj: " + mj + ", mn: " 
//		+ mn +
//                ", ab: " + ab + ", ex: " + ex + ", rf: " + rf);

            String title = s.substring(0, so);
            doc.add(Field.Text("title", title));
            contents = title;

            if (mj != -1 && mj < mn) // not all documents have major
subject
            {
                String major = s.substring(mj+4, mn);
//                doc.add(Field.Text("major", major));
                contents = contents + " " + major;
            }

            if (ab != -1 && ab < rf) // if this document has an abstract
            {
                abex = ab;
                String abs = s.substring(ab+4, rf);
//                doc.add(Field.Text("abstract", abs));
                contents = contents + " " + abs;
            }
            else // it has an extract instead
            {
                abex = ex;
                String extract = s.substring(ex+4, rf);
//                doc.add(Field.Text("extract", extract));
                contents = contents + " " + extract;
            }

            if (mn != -1 && mn < abex)
            {
                String minor = s.substring(mn+4, abex);
//                doc.add(Field.Text("minor", minor));
                contents = contents + " " + minor;
            }

            // add a field that's the concatenation of the others so that
            // we can search on all fields simultaneously
            doc.add(Field.Text("contents", contents));

            // DEBUG
//            System.out.println(contents);
            System.out.println(doc.toString());

            ti = s.indexOf("\nTI ");
            vdocs.add(doc);
        }

        Document[] docs = new Document[vdocs.size()];
        vdocs.toArray(docs);

        return docs;
  }

  private FileCFDocument() {}
}

// IndexCFFiles.java (a modification of the IndexFiles.java example)
import org.apache.lucene.analysis.StopAnalyzer;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.document.Document;

import java.io.File;
import java.util.Date;

// DEBUG
import org.apache.lucene.index.IndexReader;
import java.util.Vector;
import org.apache.lucene.index.TermEnum;

class IndexCFFiles
{

    public static void main(String[] args)
    {
        try
        {
            Date start = new Date();

            String indexID = "index";
            if (args.length > 1)
                indexID = args[1];
            IndexWriter writer = new IndexWriter(indexID, new
                ThoroughAnalyzer(), true);
            writer.mergeFactor = 20;

            indexDocs(writer, new File(args[0]));

            writer.optimize();
            writer.close();

            Date end = new Date();

            System.out.print(end.getTime() - start.getTime());
            System.out.println(" total milliseconds");

            // DEBUG
            // open the specified index
            IndexReader ir = IndexReader.open(indexID);

            // get an enumeration of the terms in the index
            TermEnum te = ir.terms();

            // extract the terms from this enumeration
            Vector v = new Vector();
            while (te.next())
            {
                char c = te.term().text().charAt(0);
                if (((c >= 65 && c <= 91) || (c >= 97 && c <=
123)))
                    v.add(te.term());
            }

            // place the terms in an array
            int n = v.size();

            // DEBUG
            System.out.println("Number of unique terms in index '" +
		indexID +
                          "': " + n);

        }
        catch (Exception e)
        {
            System.out.println(" caught a " + e.getClass() +
                "\n with message: " + e.getMessage());
        }
    }

    public static void indexDocs(IndexWriter writer, File file)
       throws Exception
    {
        if (file.isDirectory())
        {
            String[] files = file.list();
            for (int i = 0; i < files.length; i++)
                indexDocs(writer, new File(file, files[i]));
        }
        else
        {
            System.out.println("adding " + file);
            Document[] docs = FileCFDocument.makeDocuments(file);
            for (int i = 0; i < docs.length; i++)
                writer.addDocument(docs[i]);
        }
    }
}


 jmadden@ics.uci.edu...Obscurium Per Obscurius...www.ics.uci.edu/~jmadden
    Joshua Madden: Information Scientist, Musician, Philosopher-At-Tall
 It's that moment of dawning comprehension that I live for--Bill Watterson
My opinions are too rational and insightful to be those of any organization.



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