Background
I'm using dplyr to do some data analysis. I've got this dataframe d:
d <- data.frame(ID = c("ab24","c56","kl90","ab24","c56","kl90","ab24","c56","kl90","ab24","c56","kl90","ab24","c56","kl90"),
category = c("drivetrain","drivetrain","drivetrain","drivetrain","drivetrain","drivetrain","drivetrain","drivetrain","engine","engine","engine","engine","engine","engine","engine"),
part = c("gear oil","gear oil","gear oil","cv axle","cv axle","transfer case fluid","cv intermediate shaft","differential seal","oil","exhaust valve","oil","oil","exhaust valve","piston","oil pan"),
stringsAsFactors=FALSE)
As you can see, it's about car parts: it's got some customer IDs, some part categorys, and some individual part names.
The Problem
I'd like to get a dataframe (or any table) that displays the top n -- let's say 2 -- most frequent individual parts per part category, and arrange them in descending order within part category. I have in mind something like this:
| Category | Part | n |
|------------|-----------------|-----------|
| drivetrain | gear oil | 3 |
| drivetrain | cv axle | 2 |
| engine | oil | 3 |
| engine | exhaust valve | 2 |
What I've tried
I can get something going with group_by and count, like so:
d %>%
group_by(category, part) %>%
count(part) %>%
as.data.frame() %>%
na.omit
category part n
drivetrain cv axle 2
drivetrain cv intermediate shaft 1
drivetrain differential seal 1
drivetrain gear oil 3
drivetrain transfer case fluid 1
engine exhaust valve 2
engine oil 3
engine oil pan 1
engine piston 1
But when I try throwing in a variant of slice in the code to get the 2 most frequent parts per category, I get errors like Error in slice_max(): ! argument order_by is missing, with no default. Not sure where to throw in order_by.
