Match an argument to a character vector
This is equivalent to base::match.arg() with a few differences:
Partial matches trigger an error.
Error messages are a bit more informative and obey the tidyverse standards.
arg_match() derives the possible values from the
caller frame.
arg_match0() is a bare-bones version if performance is at a premium.
It requires a string as arg and explicit values.
For convenience, arg may also be a character vector containing
every element of values, possibly permuted.
In this case, the first element of arg is used.
arg_match(arg, values = NULL) arg_match0(arg, values, arg_nm = as_label(substitute(arg)))
arg |
A symbol referring to an argument accepting strings. |
values |
The possible values that |
arg_nm |
The label to be used for |
The string supplied to arg.
fn <- function(x = c("foo", "bar")) arg_match(x)
fn("bar")
# Throws an informative error for mismatches:
try(fn("b"))
try(fn("baz"))
# Use the bare-bones version with explicit values for speed:
arg_match0("bar", c("foo", "bar", "baz"))
# For convenience:
fn1 <- function(x = c("bar", "baz", "foo")) fn3(x)
fn2 <- function(x = c("baz", "bar", "foo")) fn3(x)
fn3 <- function(x) arg_match0(x, c("foo", "bar", "baz"))
fn1()
fn2("bar")
try(fn3("zoo"))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.