I am confused by the use of the ellipsis (...
) in some functions, i.e. how to pass an object containing the arguments as a single argument.
In Python it is called "unpacking argument lists", e.g.
>>> range(3, 6) # normal call with separate arguments
[3, 4, 5]
>>> args = [3, 6]
>>> range(*args) # call with arguments unpacked from a list
[3, 4, 5]
In R for instance you have the function file.path(...)
that uses an ellipsis. I would like to have this behaviour:
> args <- c('baz', 'foob')
> file.path('/foo/bar/', args)
[1] 'foo/bar/baz/foob'
Instead, I get
[1] 'foo/bar/baz' 'foo/bar/foob'
where the elements of args
are not "unpacked" and evaluated at the same time. Is there a R equivalent to Pythons *arg
?
The syntax is not as beautiful, but this does the trick:
do.call(file.path,as.list(c("/foo/bar",args)))
do.call
takes two arguments: a function and a list of arguments to call that function with.