match.arg(arg) match.arg(arg, choices)
arg
| a character string |
choices
| a character vector of candidate values |
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.
pmatch
## 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 ...