R help - Jun 2005 - parsing '...' function argument?

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).

Thanks
Oleg
--
Dr Oleg Sklyar
European Bioinformatics Institute
Wellcome Trust Genome Campus
Hinxton, Cambridge
CB10 1SD
United Kingdom

tel +44 1223 492537
fax +44 1223 494468
email osklyar@ebi.ac.uk

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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