match.arg {base} | 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.
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)