Drop unused levels from a data frame in R

Question

Consider the following dataframe

set.seed(123)
x <- data.frame(let = sample(letters[1:6], 100, replace = T), 
                num = sample(1:10, 100, replace = T))
y <- subset(x, let != 'a')

So, how can I drop unused levels i.e. those levels that are not used in the data frame?

Answer 1

You can use this command droplevels()

y <- droplevels(y)