it.unimi.di.mg4j.search.score
Class TfIdfScorer

java.lang.Object
  it.unimi.di.mg4j.search.score.AbstractScorer
      it.unimi.di.mg4j.search.score.AbstractWeightedScorer
          it.unimi.di.mg4j.search.score.TfIdfScorer

All Implemented Interfaces:

DelegatingScorer, Scorer, FlyweightPrototype<Scorer>

public class TfIdfScorer
extends AbstractWeightedScorer
implements DelegatingScorer

A scorer that implements the TF/IDF ranking formula.

There are a number of incarnations with small variations of the formula itself. Here, the weight assigned to a term which appears in f documents out of a collection of N documents w.r.t. to a document of length l in which the term appears c times is

log(N / f) c / l,

This class uses a CounterCollectionVisitor and related classes to take into consideration only terms that are actually involved in the current document.

Author:

Sebastiano Vigna

Field Summary

Fields inherited from class it.unimi.di.mg4j.search.score.AbstractWeightedScorer

index2Weight

Fields inherited from class it.unimi.di.mg4j.search.score.AbstractScorer

documentIterator, indexIterator

Constructor Summary

TfIdfScorer()

Method Summary

TfIdfScorer	copy()
double	score() Computes a score by calling Scorer.score(Index) for each index in the current document iterator, and adding the weighted results.
double	score(Index index) Returns a score for the current document of the last document iterator given to Scorer.wrap(DocumentIterator), but considering only a given index (optional operation).
boolean	usesIntervals() Whether this scorer uses intervals.
void	wrap(DocumentIterator d) Wraps the given document iterator.

Methods inherited from class it.unimi.di.mg4j.search.score.AbstractWeightedScorer

getWeights, setWeights

Methods inherited from class it.unimi.di.mg4j.search.score.AbstractScorer

nextDocument

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface it.unimi.di.mg4j.search.score.Scorer

getWeights, nextDocument, setWeights

Constructor Detail

TfIdfScorer

public TfIdfScorer()

Method Detail

copy

public TfIdfScorer copy()

Specified by:

copy in interface DelegatingScorer

Specified by:

copy in interface Scorer

Specified by:

copy in interface FlyweightPrototype<Scorer>

score

public double score()
             throws IOException

Description copied from class: AbstractWeightedScorer

Computes a score by calling Scorer.score(Index) for each index in the current document iterator, and adding the weighted results.

Specified by:

score in interface Scorer

Overrides:

score in class AbstractWeightedScorer

Returns:

the combined weighted score.

Throws:

IOException

score

public double score(Index index)

Description copied from interface: Scorer

Returns a score for the current document of the last document iterator given to Scorer.wrap(DocumentIterator), but considering only a given index (optional operation).

Specified by:

score in interface Scorer

Parameters:

index - the only index to be considered.

Returns:

the score.

wrap

public void wrap(DocumentIterator d)
          throws IOException

Description copied from class: AbstractScorer

Wraps the given document iterator.

This method records internally the provided iterator.

Specified by:

wrap in interface Scorer

Overrides:

wrap in class AbstractWeightedScorer

Parameters:

d - the document iterator that will be used in subsequent calls to Scorer.score() and Scorer.score(Index).

Throws:

IOException

usesIntervals

public boolean usesIntervals()

Description copied from interface: Scorer

Whether this scorer uses intervals.

This method is essential when aggregating scorers, because if several scores need intervals, a CachingDocumentIterator will be necessary.

Specified by:

usesIntervals in interface Scorer

Returns:

true if this scorer uses intervals.