Examples of org.apache.lucene.search.similarities.TFIDFSimilarity.idf()

org.apache.lucene.search.similarities.TFIDFSimilarity.idf()

Computes a score factor based on a term's document frequency (the number of documents which contain the term). This value is multiplied by the {@link #tf(int)} factor for each term in the query and these products arethen summed to form the initial score for a document.

Terms that occur in fewer documents are better indicators of topic, so implementations of this method usually return larger values for rare terms, and smaller values for common terms. @param docFreq the number of documents which contain the term @param numDocs the total number of documents in the collection @return a score factor based on the term's document frequency

    TFIDFSimilarity sim = asTFIDF(searcher.getSimilarity(), field);
    if (sim == null) {
      throw new UnsupportedOperationException("requires a TFIDFSimilarity (such as DefaultSimilarity)");
    }
    int docfreq = searcher.getIndexReader().docFreq(new Term(indexedField, indexedBytes));
    float idf = sim.idf(docfreq, searcher.getIndexReader().maxDoc());
    return new ConstDoubleDocValues(idf, this);
  }
  
  // tries extra hard to cast the sim to TFIDFSimilarity
  static TFIDFSimilarity asTFIDF(Similarity sim, String field) {

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