#-------------------
# Association Rules
#-------------------
library(arules)

#Groceries data
data(Groceries)

#Create an item frequency plot for the top 20 items
itemFrequencyPlot(Groceries, topN=20, type="absolute")

#Get the rules
rules <- apriori(Groceries, parameter = list(supp = 0.001, conf = 0.8))

#Show the top 5 rules, but only 2 digits
options(digits=2)
inspect(rules[1:5])

#Sort rules by confidence
rules <- sort(rules, by="confidence", decreasing=TRUE)
inspect(rules[1:5])

#Rules with max length of 3
rules <- apriori(Groceries, parameter = list(supp = 0.001, conf = 0.8, maxlen=3))
inspect(rules[1:5])



Source: 
http://www.salemmarafi.com/code/market-basket-analysis-with-r/