Assigning to a quosure in R / dplyr / rlang

Question

Within a function, I want to update-in-place the values of columns specified by the user, where the user specified column names are captured via enquo(). So, here's a simplified example:

f1 <- function(df, x, y) {
    x <- enquo(x)
    y <- enquo(y)

    df %>%
        mutate((!! x) := (!! x)^2,
               (!! y) := (!! y)+1)
}

dat <- data.frame(a=1:10, b=10:1)
f1(dat, x=a, y=b)

This fails with an error: "The LHS of := must be a string or a symbol".

I've also tried replacing, for example, (!! x) with quo_get_expr(x) and f_text(x), but get the same error. For example:

f1 <- function(df, x, y) {
    x <- enquo(x)
    y <- enquo(y)

    df %>%
        mutate(quo_get_expr(x) := (!! x)^2,
               quo_get_expr(y) := (!! y)+1)
}

Can anyone point out what I'm doing wrong?

I'm using R 4.1, dplyr 0.7.4, and rlang 0.2.0

Thanks in advance.

Answer 1

You need to use quo_name. This works:

f1 <- function(df, x, y) {
  x <- enquo(x)
  y <- enquo(y)

  df %>%
    mutate(
     !!quo_name(x) := (!!x)^2,
     !!quo_name(y) := (!!y)+1)
}

dat <- data.frame(a=1:10, b=10:1)
f1(dat, x=a, y=b)