call
or
call(...)
.
call(NAME, ...) is.call(x) as.call(x)
call
creates a call to the named function, using the remaining
arguments as the arguments to the function call.
is.call
checks whether
x
is a function call
as.call
tries to coerce
x
to a function call.
The
as.call
function is generic; currently there are no methods written
for it.
One use of
call
is in functions that create other functions.
The
d.order
example below is a non-trivial example;
d.order
is a
function that creates the density function of an order statistic from
a sample from a specific distribution.
funs <- c("sin", "cos") x <- 30*pi/180 i <- 1 my.call <- call(funs[i], as.name("x")) # my.call ready to be evaluated or put into an expression eval (my.call) # function that creates the density function of an order statistic d.order <- function(n, r, distfun, densityfun) { f <- function(x) NULL con <- exp(lgamma(n + 1) - lgamma(r) - lgamma(n - r + 1)) c1 <- call(substitute(distfun), as.name("x")) c2 <- call("^", call("-", 1, c1), n - r) c3 <- call("^", c1, r - 1) c4 <- call("*", con, call("*", c2, call("*", c3, call(substitute( densityfun), as.name("x"))))) f[[length(f)]] <- c4 f } d.median.norm.9 <- d.order(9, 5, pnorm, dnorm) d.median.norm.9(-2:2)