org.lenskit.similarity

Class PearsonCorrelation

java.lang.Object

org.lenskit.similarity.PearsonCorrelation

All Implemented Interfaces:

java.io.Serializable, VectorSimilarity

@Shareable
 @ThreadSafe
public class PearsonCorrelation
extends java.lang.Object
implements VectorSimilarity, java.io.Serializable

Similarity function using Pearson correlation.

This class implements the Pearson correlation similarity function over sparse vectors. Only the items occurring in both vectors are considered when computing the variance.

See Desrosiers, C. and Karypis, G., A Comprehensive Survey of Neighborhood-based Recommendation Methods. In Ricci, F., Rokach, L., Shapira, B., and Kantor, P. (eds.), Recommender Systems Handbook, Springer. 2010, pp. 107-144.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
PearsonCorrelation()
PearsonCorrelation(double s)

Method Summary

Modifier and Type	Method and Description
boolean	isSparse() Query whether this similarity function is sparse (returns 0 for vectors with disjoint key sets).
boolean	isSymmetric() Query whether this similarity function is symmetric.
double	similarity(Long2DoubleMap vec1, Long2DoubleMap vec2) Compute the similarity between two vectors.
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

PearsonCorrelation

public PearsonCorrelation()

PearsonCorrelation

@Inject
public PearsonCorrelation(@SimilarityDamping
                                  double s)

Method Detail

similarity

public double similarity(Long2DoubleMap vec1,
                         Long2DoubleMap vec2)

Description copied from interface: VectorSimilarity

Compute the similarity between two vectors.

Specified by:

similarity in interface VectorSimilarity

Parameters:

vec1 - The left vector to compare.

vec2 - The right vector to compare.

Returns:

The similarity, in the range [-1,1].

isSparse

public boolean isSparse()

Description copied from interface: VectorSimilarity

Query whether this similarity function is sparse (returns 0 for vectors with disjoint key sets).

Specified by:

isSparse in interface VectorSimilarity

Returns:

true iff VectorSimilarity.similarity(Long2DoubleMap, Long2DoubleMap) will always return true when applied to two vectors with no keys in common.

isSymmetric

public boolean isSymmetric()

Description copied from interface: VectorSimilarity

Query whether this similarity function is symmetric. Symmetric similarity functions return the same result when called on (A,B) and (B,A).

Specified by:

isSymmetric in interface VectorSimilarity

Returns:

true if the function is symmetric.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object