Functions like starts_with(), contains() or matches() are
selection helpers that only work in a selection context, e.g.
dplyr::select() or the cols argument of tidyr::pivot_longer().
Using a selection helper anywhere else results in an error:
starts_with("foo")
#> Error:
#> ! `starts_with()` must be used within a *selecting* function.
#> i See
#> <https://tidyselect.r-lib.org/reference/faq-selection-context.html>
#> for details.mtcars[contains("foo")]
#> Error:
#> ! `contains()` must be used within a *selecting* function.
#> i See
#> <https://tidyselect.r-lib.org/reference/faq-selection-context.html>
#> for details.
subset(mtcars, select = matches("foo"))
#> Error:
#> ! `matches()` must be used within a *selecting* function.
#> i See
#> <https://tidyselect.r-lib.org/reference/faq-selection-context.html>
#> for details.
If you see this error, you may have used a selection helper in the wrong place, possibly as the result of a typo (e.g. misplaced comma or wrong argument name). Alternatively, you may be deliberately trying to reduce duplication in your code by extracting out a selection into a variable:
my_vars <- c(name, species, ends_with("color"))
#> Error in eval(expr, envir, enclos): object 'name' not found
To make this work you’ll need to do two things:
Wrap the whole thing in a function
Use any_of() or all_of() instead of bare variable names
my_vars <- function() {
c(any_of(c("name", "species")), ends_with("color"))
}
dplyr::select(starwars, my_vars())
#> # A tibble: 87 x 5
#> name species hair_color skin_color eye_color
#> <chr> <chr> <chr> <chr> <chr>
#> 1 Luke Skywalker Human blond fair blue
#> 2 C-3PO Droid <NA> gold yellow
#> 3 R2-D2 Droid <NA> white, blue red
#> 4 Darth Vader Human none white yellow
#> # i 83 more rows