match.call
Argument Matching
match.call returns a call in which all of the specified arguments are
specified by their full names.
- Keywords
- programming
Usage
match.call(definition = sys.function(sys.parent()),
call = sys.call(sys.parent()),
expand.dots = TRUE,
envir = parent.frame(2L))Arguments
- definition
a function, by default the function from which
match.callis called. See details.- call
an unevaluated call to the function specified by
definition, as generated bycall.- expand.dots
logical. Should arguments matching
…in the call be included or left as a…argument?- envir
an environment, from which the
…incallare retrieved, if any.
Details
‘function’ on this help page means an interpreted function
(also known as a ‘closure’): match.call does not support
primitive functions (where argument matching is normally
positional).
match.call is most commonly used in two circumstances:
To record the call for later re-use: for example most model-fitting functions record the call as element
callof the list they return. Here the defaultexpand.dots = TRUEis appropriate.To pass most of the call to another function, often
model.frame. Here the common idiom is thatexpand.dots = FALSEis used, and the…element of the matched call is removed. An alternative is to explicitly select the arguments to be passed on, as is done inlm.
Calling match.call outside a function without specifying
definition is an error.
Value
An object of class call.
References
Chambers, J. M. (1998) Programming with Data. A Guide to the S Language. Springer.
See Also
sys.call() is similar, but does not expand the
argument names;
call, pmatch, match.arg,
match.fun.
Examples
library(base)
# NOT RUN {
match.call(get, call("get", "abc", i = FALSE, p = 3))
## -> get(x = "abc", pos = 3, inherits = FALSE)
fun <- function(x, lower = 0, upper = 1) {
structure((x - lower) / (upper - lower), CALL = match.call())
}
fun(4 * atan(1), u = pi)
# }