match.arg {base}R Documentation

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.


match.arg(arg, choices, several.ok = FALSE)


arg a character vector (of length one unless several.ok is TRUE) or NULL.
choices a character vector of candidate values
several.ok logical specifying if arg should be allowed to have more than one element.


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.


The unabbreviated version of the 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 there is more than one match, all unabbreviated versions of matches are returned.

See Also



## Extends the example for 'switch'
center <- function(x, type = c("mean", "median", "trimmed")) {
  type <- match.arg(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)

[Package base version 2.5.0 Index]