Apply a custom function to any number of columns using dplyr

I'm following this example in the dplyr site to program a function that aplies to any number of user supplied columns.

Here is a reprex:

library(tidyverse)
library(palmerpenguins)

trim_whitespace <- function(.data, ...) {
  .data |> mutate(across(..., \(x) str_remove_all(x, "\\s")))
}

# Add whitespace at the end of chr columns
penguins_with_whitespace <- 
  penguins |>
  mutate(across(c(species, island), \(x) paste0(x, " ")))

penguins_with_whitespace |> trim_whitespace(species, island)

This causes the error: 'island' not found. Why is this function not working and what would be the way to fix it?

Solution

Basically across thinks you are feeding it island as an object rather than a column in the penguins dataset. The way around it is just to add c(...) or {{}} to the function like this

library(tidyverse)
library(palmerpenguins)

## what the function thinks it is doing 
penguins |>
  mutate(across(species,island, \(x) str_remove_all(x, '\\s')))
#> Error in `mutate()`:
#> ℹ In argument: `across(species, island, function(x) str_remove_all(x,
#>   "\\s"))`.
#> Caused by error:
#> ! object 'island' not found


f1 <- function(.data, ... ) {
  .data |> mutate(across(c(...), \(x) str_remove_all(x, "\\s")))
}


f2  <- function(.data, cols ) {
  .data |> mutate(across({{cols}}, \(x) str_remove_all(x, "\\s")))
}



penguins |>
  f1(species, island) |>
  head(1)
#> # A tibble: 1 × 8
#>   species island    bill_length_mm bill_depth_mm flipper_length_mm body_mass_g
#>   <chr>   <chr>              <dbl>         <dbl>             <int>       <int>
#> 1 Adelie  Torgersen           39.1          18.7               181        3750
#> # ℹ 2 more variables: sex <fct>, year <int>

penguins |>
  f2(c(species, island)) |>
  head(1)
#> # A tibble: 1 × 8
#>   species island    bill_length_mm bill_depth_mm flipper_length_mm body_mass_g
#>   <chr>   <chr>              <dbl>         <dbl>             <int>       <int>
#> 1 Adelie  Torgersen           39.1          18.7               181        3750
#> # ℹ 2 more variables: sex <fct>, year <int>

^{Created on 2024-12-02 with reprex v2.1.1}