Count number of words in a Dictionary file in R

I am reading in a dictionary into R via the quanteda package. This package is preloaded with some great dictionaries, one of which is the Moral Foundations Dictionary that I am interested in. This dictionary has several categories (Farm, Fairness, Ingroup etc.) which are broken down to virtue and vice subcategories.

I want to count the number of words that are in each subcategory for each foundation in R. How can I go about doing that?

For a reproducible example, I can access the Moral Foundations Dictionary (labeled as data_dictionary_MFD) by running library(quanteda.dictionaries)

Thank you!