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rtidyversetidyselect

Pass vector of unquoted column names to a function and use first element

This works as expected:

library(dplyr)

f <- function(x = c(am, vs)) 
  mtcars %>% 
    select({{x}})

How would I rewrite the function (let's call it f2) such that f2 selects only the first element of x, that is f2() should eventually be the same as mtcars %>% select(am)?

Some requirements:

  • I do want to pass the columns as vector, thus a solution using ... would not work in my case.
  • I want to stay inside the tidyverse syntax and want to pass unquoted column names, that is using x = c("am", "vs") is also not desired.
Solution

  • tidyselect::eval_select() returns a vector of indices used by select() that can be subset, so one approach might be:

    library(tidyselect)
library(dplyr)

f2 <- function(x = c(am, vs)){
  mtcars %>%
    select(first(eval_select(expr({{x}}), data = .)))
}

f2() |>
  names()

[1] "am"