# match.arg

##### Argument Verification Using Partial Matching

`match.arg`

matches `arg`

against a table of candidate
values as specified by `choices`

, where `NULL`

means to take
the first one.

- Keywords
- programming

##### Usage

`match.arg(arg, choices, several.ok = FALSE)`

##### Arguments

- arg
a character vector (of length one unless

`several.ok`

is`TRUE`

) or`NULL`

.- choices
a character vector of candidate values

- several.ok
logical specifying if

`arg`

should be allowed to have more than one element.

##### Details

In the one-argument form `match.arg(arg)`

, the choices are
obtained from a default setting for the formal argument `arg`

of
the function from which `match.arg`

was called. (Since default
argument matching will set `arg`

to `choices`

, this is
allowed as an exception to the ‘length one unless
`several.ok`

is `TRUE`

’ rule, and returns the first
element.)

Matching is done using `pmatch`

, so `arg`

may be
abbreviated.

##### Value

The unabbreviated version of the exact or unique partial match if
there is one; otherwise, an error is signalled if `several.ok`

is
false, as per default. When `several.ok`

is true and more than
one element of `arg`

has a match, all unabbreviated versions of
matches are returned.

##### See Also

##### Examples

`library(base)`

```
# NOT RUN {
require(stats)
## Extends the example for 'switch'
center <- function(x, type = c("mean", "median", "trimmed")) {
type <- match.arg(type)
switch(type,
mean = mean(x),
median = median(x),
trimmed = mean(x, trim = .1))
}
x <- rcauchy(10)
center(x, "t") # Works
center(x, "med") # Works
try(center(x, "m")) # Error
stopifnot(identical(center(x), center(x, "mean")),
identical(center(x, NULL), center(x, "mean")) )
## Allowing more than one match:
match.arg(c("gauss", "rect", "ep"),
c("gaussian", "epanechnikov", "rectangular", "triangular"),
several.ok = TRUE)
# }
```

*Documentation reproduced from package base, version 3.6.1, License: Part of R 3.6.1*