arg_element: Check Element

In arg: Clean and Simple Argument Checking

Check Element

Description

Checks whether values in an argument are all elements of some set (arg_element()) or are not all elements of a set (arg_not_element()). arg_element() throws an error when all(is.element(x, values)) is FALSE, and arg_not_element() throws an error when any(is.element(x, values)) is TRUE.

Usage

arg_element(x, values, .arg = rlang::caller_arg(x), .msg = NULL, .call)

arg_not_element(x, values, .arg = rlang::caller_arg(x), .msg = NULL, .call)

Arguments

x	the argument to be checked
values	the values to check x against.
.arg	the name of the argument supplied to x to appear in error messages. The default is to extract the argument's name using rlang::caller_arg(). Ignored if .msg is supplied.
.msg	an optional alternative message to display if an error is thrown instead of the default message.
.call	the execution environment of a currently running function, e.g. .call = rlang::current_env(). The corresponding function call is retrieved and mentioned in error messages as the source of the error. Passed to err(). Set to NULL to omit call information. The default is to search along the call stack for the first user-facing function in another package, if any.

Details

arg_element() can be useful for checking whether an argument matches one or more allowed values. It's important that a check is done beforehand to ensure x is the correct type, e.g., using arg_string() or arg_character() if values is a character vector. No partial matching is used; the values must match exactly. Use match_arg() to allow partial matching and return the full version of the supplied argument.

arg_not_element() can be useful for ensuring there is no duplication of values between an argument and some other set.

Value

Returns NULL invisibly if an error is not thrown.

See Also

is.element(), match_arg()

Examples

f <- function(z) {
  arg_element(z, c("opt1", "opt2", "opt3"))
}

try(f("opt1"))            # No error
try(f(c("opt1", "opt2"))) # No error, all are elements
try(f(c("opt1", "opt1"))) # No error: repeats allowed
try(f("bad_arg"))         # Error: not an element of set
try(f("opt"))             # Error: partial matching not allowed
try(f(c("opt1", "bad_arg"))) # Error: one non-match

g <- function(z) {
  arg_not_element(z, c("bad1", "bad2", "bad3"))
}

try(g("bad1"))            # Error: z is an element
try(g(c("bad1", "opt2"))) # Error: at least one bad match
try(g("opt1"))            # No error: not an element
try(g(c("opt1", "opt2"))) # No error, none are elements

arg documentation built on April 9, 2026, 5:09 p.m.