I am attempting to reproduce one of the examples in the dplyr package but am getting this error message. I am expecting to see a new column n produced with the frequency of each combination. What am I missing? I triple checked that the package is loaded.
library(dplyr)
# summarise peels off a single layer of grouping
by_vs_am <- group_by(mtcars, vs, am)
by_vs <- summarise(by_vs_am, n = n())
Error in n() : This function should not be called directly