Arules returning empty LHS

Question

I have a dataset which looks like this:

"user.get","search_restaurants","cuisines.get"
"user.get","search_restaurants","user.get","search_restaurants"
"order/address/get_user_addresses"
"search_restaurants","search_restaurantssearch_restaurants"
"restaurant.get","search_restaurants","order/menu","restaurant.get","restaurant.get","restaurant.get","order/menu","order/menu","restaurant.get","restaurant.getsearch_restaurantsrestaurant.get","user.get","order/menu","order/menu","get_user_reviews_filtered","order/menu","restaurant.get"

When I run the apriori algorithm on it:

txn1 = read.transactions(file="path", rm.duplicates=TRUE)
basket_rules <- apriori(txn1, parameter = list(sup = 0.01, conf = 0.01,target="rules"))
inspect(basket_rules)

I get blank lhs's. which are:

{} => {cuisines.get}, etc

Any idea why this might be happening? An how to solve this issue?

Answer 1

From help("apriori"):

The default value in APparameter for minlen is 1. This means that rules with only one item (i.e., an empty antecedent/LHS) like

{} => {beer}

will be created. These rules mean that no matter what other items are involved the item in the RHS will appear with the probability given by the rule's confidence (which equals the support). If you want to avoid these rules then use the argument parameter=list(minlen=2).