| match.arg | R Documentation |
match.arg matches arg against a table of candidate
values as specified by choices, where NULL means to take
the first one.
match.arg(arg, choices, several.ok = FALSE)
arg |
a character vector (of length one unless |
choices |
a character vector of candidate values |
several.ok |
logical specifying if |
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.
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.
The error messages given are liable to change and will do so in R 4.2.0. Do not test them in packages.
pmatch,
match.fun,
match.call.
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)
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