I am trying to provide two functions inside the mutate(across(where(is.factor))) to order the factor levels and drop unused levels. The code appears not to be working as expected. Where might have gone wrong?

#---- Libraries ----

library(tidyverse)

#---- Data ----

set.seed(2021)

df <- tibble(
  a1 = factor(ifelse(sign(rnorm(30))==-1, 0, 1), labels = c("No", "Yes")),
  a2 = factor(ifelse(sign(rnorm(30))==-1, 0, 1), labels = c("No", "Yes")),
  gender = gl(2, 15, labels = c("Males", "Females")),
  b2 = gl(3, 10, labels = c("Primary", "Secondary", "Tertiary", "Unknown")),
  c1 = gl(3, 10, labels = c("15-19", "20-24", "25-30", "30-35")),
  outcome = factor(ifelse(sign(rnorm(30))==-1, 0, 1), labels = c("No", "Yes")),
  weight = runif(30, 1, 12)
)

#---- Problem ----

df <- df %>%
  mutate(across(where(is.factor), list(fct_infreq, fct_drop)))

levels(df$b2)

# The unused levels not dropped

回答

df <- df %>%
  mutate(across(where(is.factor), fct_drop)) %>% 
  mutate(across(where(is.factor), fct_infreq)) 
  

df <- df %>%
  mutate(across(where(is.factor), ~fct_infreq(fct_drop(.x))))