Converting multiple columns to factors and releveling with mutate(across) - r

Question

dat <- data.frame(Comp1Letter = c("A", "B", "D", "F", "U", "A*", "B", "C"),
Comp2Letter = c("B", "C", "E", "U", "A", "C", "A*", "E"),
Comp3Letter = c("D", "A", "C", "D", "F", "D", "C", "A"))
GradeLevels <- c("A*", "A", "B", "C", "D", "E", "F", "G", "U")
I have a dataframe that looks something like the above (but with many other columns I don't want to change).
The columns I am interested in changing contains lists of letter grades, but are currently character vectors and not in the right order.
I need to convert each of these columns into factors with the correct order. I've been able to get this to work using the code below:
factordat <-
dat %>%
mutate(Comp1Letter = factor(Comp1Letter, levels = GradeLevels)) %>%
mutate(Comp2Letter = factor(Comp2Letter, levels = GradeLevels)) %>%
mutate(Comp3Letter = factor(Comp3Letter, levels = GradeLevels))
However this is super verbose and chews up a lot of space.
Looking at some other questions, I've tried to use a combination of mutate() and across(), as seen below:
factordat <-
dat %>%
mutate(across(c(Comp1Letter, Comp2Letter, Comp3Letter) , factor(levels = GradeLetters)))
However when I do this the vectors remain character vectors.
Could someone please tell me what I'm doing wrong or offer another option?

Answer 1

You can do across as an anonymous function like this:
dat <- data.frame(Comp1Letter = c("A", "B", "D", "F", "U", "A*", "B", "C"),
Comp2Letter = c("B", "C", "E", "U", "A", "C", "A*", "E"),
Comp3Letter = c("D", "A", "C", "D", "F", "D", "C", "A"))
GradeLevels <- c("A*", "A", "B", "C", "D", "E", "F", "G", "U")
dat %>%
tibble::as_tibble() %>%
dplyr::mutate(dplyr::across(c(Comp1Letter, Comp2Letter, Comp3Letter) , ~forcats::parse_factor(., levels = GradeLevels)))
# # A tibble: 8 × 3
# Comp1Letter Comp2Letter Comp3Letter
# <fct> <fct> <fct>
# 1 A B D
# 2 B C A
# 3 D E C
# 4 F U D
# 5 U A F
# 6 A* C D
# 7 B A* C
# 8 C E A
You were close, all that was left to be done was make the factor function anonymous. That can be done either with ~ and . in tidyverse or function(x) and x in base R.