[R] parsing '...' function argument?

[Gabor Grothendieck]

On 6/30/05, Oleg Sklyar <osklyar at ebi.ac.uk> wrote:
> Dear community,
> 
> I am writing a wrapper for '[' operator, which is a generic method
> declared as function(x, i, j, ..., drop). It turns out that I need to
> parse the '...' argument and this is where I am stuck. Generally what I
> need is the following. Say the call is obj[1, 1, 1:10, 3] - here '1:10,
> 3' is passed into '...'. What I need to evaluate that '...' contains now
> 2 arguments, first is a vector of 10 elements and second is a single
> value. Even nicer situation is in call obj[1, 1, , 3] - where ' , 3' is
> passed in '...' with one missing argument, which for an array would mean
> the full range. Any ideas? (Just to mention - if there were only one
> argument in '...', say '1:10', then length(...) would return 10 and one
> could access elements by ...[[i]], but all this fails if there are two
> arguments or more).
> 

Check out the technique used in this post:

http://tolstoy.newcastle.edu.au/R/help/04/06/1430.html