How to count number of values in columns based on a category in R?

Suppose we have a data frame df like

book_id book_category book_word_hi book_word_bye book_word_yes
1       drama         3            0             4
2       action        1            4             5
3       drama         5            3             2

I would like to count the number of values within the book_word columns and sum them in a table for each book_category.

So the output here should look something like:

drama: 17 
action: 10

Does anyone know how to do this?

>Solution :

This is a short and simple one-liner in base R, without requiring any additional packages.

tapply(rowSums(df[3:5]), df[2], sum)
#> book_category
#> action  drama 
#>     10     17