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do.call constructs and executes a function call from a name or
a function and a list of arguments to be passed to it.
do.call(what, args, quote = FALSE, envir = parent.frame())names attribute of args gives the argument names.what is a character string and
the arguments are symbols or quoted expressions..Internal and other non-API calls.quote is FALSE, the default, then the arguments are
evaluated (in the calling environment, not in envir). If
quote is TRUE then each argument is quoted (see
quote) so that the effect of argument evaluation is to
remove the quotes -- leaving the original arguments unevaluated when the
call is constructed. The behavior of some functions, such as substitute,
will not be the same for functions evaluated using do.call as
if they were evaluated from the interpreter. The precise semantics
are currently undefined and subject to change.
call which creates an unevaluated call.
do.call("complex", list(imag = 1:3))
## if we already have a list (e.g., a data frame)
## we need c() to add further arguments
tmp <- expand.grid(letters[1:2], 1:3, c("+", "-"))
do.call("paste", c(tmp, sep = ""))
do.call(paste, list(as.name("A"), as.name("B")), quote = TRUE)
## examples of where objects will be found.
A <- 2
f <- function(x) print(x^2)
env <- new.env()
assign("A", 10, envir = env)
assign("f", f, envir = env)
f <- function(x) print(x)
f(A) # 2
do.call("f", list(A)) # 2
do.call("f", list(A), envir = env) # 4
do.call(f, list(A), envir = env) # 2
do.call("f", list(quote(A)), envir = env) # 100
do.call(f, list(quote(A)), envir = env) # 10
do.call("f", list(as.name("A")), envir = env) # 100
eval(call("f", A)) # 2
eval(call("f", quote(A))) # 2
eval(call("f", A), envir = env) # 4
eval(call("f", quote(A)), envir = env) # 100
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