R arules, mine only rules from specific column

Question

I would like to mine specific rhs rules. There is an example in the documentation which demonstrates that this is possible, but only for a specific case (as we see below). First an data set to illustrate my problem:

input <- matrix( c( rep(10001,6) , rep(10002,3) , rep(10003,3), 100001,100002,100003,100004,100005,100006,100002,100003,100007,100002,100003,100008,rep('a',6),rep('b',6)), ncol=3)
colnames(input) <- c(letters[1:3])
input <- as.data.frame(input)

Now i can create rules:

 r <- apriori(input)

To see the rules:

inspect(r)

I would like to only mine rules that have b=... on the rhs. For specific values this can be done by adding:

appearance = list(rhs = c("b=100001", "b=100002"),default="lhs")

to the apriori command. I will also have to adjust the confidence if i want to find them ofcourse. The problem lies in the number of elements in column b. I can manualy type all the elements in the "b=....." format in this example, but I can't in my own data.

I tried to get the values of b using unique() and then giving that to the rhs, but it will generate an error because i give values like: "100001" "100002" instead of "b=100001" "b=100002".

Is there a was to only get rhs rules from a specific column?

If not, is there an easy way to generate 'want' from 'current?

current <- c("100001", "100002", "100003", "100004", "100005", "100006", "100007", "100008")
want    <- c("b=100001", "b=100002", "b=100003", "b=100004", "b=100005", "b=100006", "b=100007", "b=100008")

Somewhat related is this question: Creating specific rules with arules in r But that has the same problem for me, only a different way.

Answer 1

You can use subset:

r <- apriori(input, parameter = list(support = 0.1, confidence = 0.1))
inspect( subset( r, subset = rhs %pin% "b=" ) )
#   lhs      rhs          support confidence     lift
# 1 {}    => {b=100002} 0.2500000  0.2500000 1.000000
# 2 {}    => {b=100003} 0.2500000  0.2500000 1.000000
# 3 {c=b} => {b=100002} 0.1666667  0.3333333 1.333333
# 4 {c=b} => {b=100003} 0.1666667  0.3333333 1.333333

For you second question, you can use paste:

paste0( "b=", current )
# [1] "b=100001" "b=100002" "b=100003" "b=100004" "b=100005" "b=100006" "b=100007"
# [8] "b=100008"