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
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