match.arg
Argument Verification Using Partial Matching
match.arg
matches arg
against a table of candidate
values as specified by choices
, where NULL
means to take
the first one.
 Keywords
 programming
Usage
match.arg(arg, choices, several.ok = FALSE)
Arguments
 arg
 a character vector (of length one unless
several.ok
isTRUE
) orNULL
.  choices
 a character vector of candidate values
 several.ok
 logical specifying if
arg
should be allowed to have more than one element.
Details
In the oneargument 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.
Value

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.
See Also
Examples
library(base)
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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