arules (version 1.0-12)

affinity: Computing Affinity Between Items

Description

Provides the generic function affinity and the S4 methods to compute and return a similarity matrix with the affinities between items for a set of transactions.

Usage

affinity(x)

Arguments

x

a matrix or an object of class itemMatrix or transactions.

Value

• returns an object of class ar_similarity which represents the affinities between items in x.

Details

Affinity between the two items $i$ and $j$ is defined by Aggarwal et al. (2002) as $$A(i,j) = \frac{sup({i,j})}{sup({i}) + sup({j}) - sup({i,j})},$$ where $sup(.)$ is the support measure. This means that affinity is the Jaccard similarity between items.

References

Charu C. Aggarwal, Cecilia Procopiuc, and Philip S. Yu (2002) Finding localized associations in market basket data, IEEE Trans. on Knowledge and Data Engineering, 14(1):51--62.

See Also

dissimilarity, ar_similarity-class, itemMatrix-class

Examples

data("Adult")

## choose a sample, calculate affinities 
s <- sample(Adult, 500)
s

a <- affinity(s)
summary(as.vector(a))