do.call
Execute a Function Call
do.call constructs and executes a function call from a name or
a function and a list of arguments to be passed to it.
- Keywords
- programming
Usage
do.call(what, args, quote = FALSE, envir = parent.frame())Arguments
- what
either a function or a non-empty character string naming the function to be called.
- args
a list of arguments to the function call. The
namesattribute ofargsgives the argument names.- quote
a logical value indicating whether to quote the arguments.
- envir
an environment within which to evaluate the call. This will be most useful if
whatis a character string and the arguments are symbols or quoted expressions.
Details
If 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.
Value
The result of the (evaluated) function call.
Warning
This should not be used to attempt to evade restrictions on the use of
.Internal and other non-API calls.
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
call which creates an unevaluated call.
Examples
library(base)
# NOT RUN {
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
# }