Question

How can I rewrite the for loop in the following piece of code using lapply?

transactions <- read.table(file = file("stdin"), header = FALSE, stringsAsFactors = FALSE)
for (i in 1:nrow(transactions)) {
  transactions[i,1] <- paste(sort(unlist(strsplit(transactions[i,1], ","))), collapse = ",")
}

If you find it easier to work with some input data, use the following as the contents of stdin:

a,b
b,c,a
a,b,c
b,a,c
a,b,c,d
a,d,b,c

Answer 1

It looks like you want to sort the individual comma-separated components of transactions[, 1].

transactions[, 1] <- sapply(lapply(strsplit(transactions[, 1], ","),
                                   sort),
                            paste, collapse=",")