Finding suitable rules for new data using arules

Question

I am using R (and the arules package) to mining transactions for association rules. What I wish to do is construct the rules and then apply them to new data.

For example, say I have many rules, one of which is the canonical {Beer=YES} -> {Diapers=YES}.

Then I have new transactional data where one of the records has purchased beer but not diapers. How can I identify a rule where the LHS is met, but not yet the RHS?

R example:

install.packages("arules")
library(arules)

data("Groceries")
**#generate Rules omitting second record**

rules <- apriori(Groceries[-2],parameter = list(supp = 0.05, conf = 0.2,target = "rules"))

Rules generated are:

> inspect(rules)
  lhs                   rhs                   support confidence     lift
1 {}                 => {whole milk}       0.25554200  0.2555420 1.000000
2 {yogurt}           => {whole milk}       0.05603010  0.4018964 1.572722
3 {whole milk}       => {yogurt}           0.05603010  0.2192598 1.572722
4 {rolls/buns}       => {whole milk}       0.05664023  0.3079049 1.204909
5 {whole milk}       => {rolls/buns}       0.05664023  0.2216474 1.204909
6 {other vegetables} => {whole milk}       0.07484238  0.3867578 1.513480
7 {whole milk}       => {other vegetables} 0.07484238  0.2928770 1.513480

The second transaction shows this customer, since they have yogurt but not whole milk perhaps should be sent a coupon for milk. How can any applicable rules in "rules" be located for new transactions?

> LIST(Groceries[2])
[[1]]
[1] "tropical fruit" "yogurt"         "coffee" 

Answer 1

The key is the is.subset-function in the same package

Here is the code ...

basket <- Groceries[2]
# find all rules, where the lhs is a subset of the current basket
rulesMatchLHS <- is.subset(rules@lhs,basket)
# and the rhs is NOT a subset of the current basket (so that some items are left as potential recommendation)
suitableRules <-  rulesMatchLHS & !(is.subset(rules@rhs,basket))

# here they are
inspect(rules[suitableRules])

# now extract the matching rhs ...
recommendations <- strsplit(LIST(rules[suitableRules]@rhs)[[1]],split=" ")
recommendations <- lapply(recommendations,function(x){paste(x,collapse=" ")})
recommendations <- as.character(recommendations)

# ... and remove all items which are already in the basket
recommendations <- recommendations[!sapply(recommendations,function(x){basket %in% x})]

print(recommendations)

and the generated output ...

> inspect(rules[suitableRules])
  lhs         rhs            support confidence     lift
1 {}       => {whole milk} 0.2555420  0.2555420 1.000000
2 {yogurt} => {whole milk} 0.0560301  0.4018964 1.572722

> print(recommendations)
[1] "whole milk"