dplyr: mutate with data from last column

Question

I want to create a new column with data from the last column of a data frame:

df <- matrix(1:4, ncol = 2) %>% as.data.frame()
df %>% mutate(V3 = .[[ncol(.)]] * 2)

Is there an easier to read and understand expression than .[[ncol(.)]]?

Answer 1

Using across and last_col you could do:

library(dplyr, warn=FALSE)

df <- matrix(1:4, ncol = 2) %>% as.data.frame()

df %>% 
  mutate(across(last_col(), ~ .x * 2, .names = "V3"))
#>   V1 V2 V3
#> 1  1  3  6
#> 2  2  4  8