在 R 的 dataframe 的某些位置添加多列

Question

I have a dataframe that looks similar to this one:

> df <- data.frame(A1=1:3, B1=1:3, A2=1:3, B2=1:3, A3=1:3, B3=1:3)
> df

  A1 B1 A2 B2 A3 B3
1  1  1  1  1  1  1
2  2  2  2  2  2  2
3  3  3  3  3  3  3

Now, I'm looking for some code that adds rows before B1, B2 and B3:

  A1 AB1 B1 A2 AB2 B2 A3 AB3 B3
1  1   X  1  1   X  1  1   X  1
2  2   X  2  2   X  2  2   X  2
3  3   X  3  3   X  3  3   X  3

As the dataframe above is only a minimum, reproducible example (the real dataframe is much larger), I'm looking for a solution either using a for loop or a solution with tidyverse. I had the idea to use a combination of a for loop and add_column from the tibble package:

library(tibble)
  
  for (i in 1:3) {
    df <- df %>%
      add_column(paste0("AB", i, "") = "X" , .before = paste0("B", i, ""))
  }

Unfortunately, the idea does not work. I'm not quite sure if the whole approach is wrong, or if there is anything wrong with the paste0() etc.. If you need any further information, please let me know. T

Answer 1

With a slight tweak your code works although there's probably better ways to do this:

for (i in 1:3) {
  df <- df %>%
    add_column(!!paste0("AB", i, collapse = "") := "X" , .before = paste0("B", i, collapse =  ""))
}