[R] function application

[Erik Iverson]

> Suppose I have a function, like list, that takes a variable number of
> arguments, and I have those arguments in some vector x.  How can execute the
> function with the *contents* of x as its arguments?  I.e., I don't want
> list(x), but rather list(x[[1]], x[[2]], ..., x[[n]]), but I don't want to
> spell out the individual elements of x (either because I want to do this
> programmatically, so I cannot code an expression like
> list(x[[1]],...,x[[n]]) because the value of n is not know until run time,
> or else, simply to avoid the tedium of typing out all the elements of x
> individually).

In this particular case, because you want to create a list,

x <- 1:10
as.list(x)

will do.

> P.S. In Python, if x is some sequence-like object (e.g. a list or a tuple),
> and f is some function, the expression f(*x) causes f to be called with the
> *contents* of x as its arguments.  (This is to be distinguished from f(x),
> which calls f with x as its sole argument.)  In Mathematica, one can achieve
> a similar effect using the Apply function: Apply[f, x].  I'm looking for the
> equivalent of this in R.

In general, if you already have a *list* and want to call a function
with the contents of that list as the arguments, then ?do.call is what
you need.

a <- list("example", "of", "do.call")

#compare the two following expressions
paste(a)
do.call(paste, a)


--Erik