match.arg                package:base                R Documentation

Argument Verification Using Partial Matching

Description:

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

Usage:

     match.arg(arg, choices)

Arguments:

     arg: a character string

 choices: a character vector of candidate values

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.

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

Value:

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

See Also:

     `pmatch', `match.fun', `match.call'.

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

