match.arg {base}

R Documentation

Argument Verification Using Partial Matching

Description

match.arg matches arg against a table of candidate values as specified by choices. 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.

Matching is done using pmatch, so arg may be abbreviated.

Usage

match.arg(arg)
match.arg(arg, choices)

Arguments

arg	a character string
choices	a character vector of candidate values

Value

The unabbreviated version of the unique partial match if there is one; otherwise, an error is signalled.

See Also

pmatch

Examples

## 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
center(x, "m")       # Error
## Actually, it would be nicer if one could catch the error
## to produce a more helpful error message ...

---