Normalizing selection of dataframe columns with dplyr

Question

I have a data.frame with variables var1 var2 (both strings) and variables x, y, and z. I would like

Answer 1

Building on @akrun's answer, you can also use the first() function from dplyr:

df_ %>%
        mutate_at(vars(c("x", "y", "z")), funs(norm = ./first(.)))