Just a minor footnote to Brian's reply below. The only place where this
kind of indexing does seem to be useful is in dealing with language objects.
lists of lists of lists ... are not all that useful, or usual, but in
language elements expressions of calls of calls of .... are the norm.
Dealing with language objects does indeed take a 'certain type' of mindset -
the kind that revels in programming puzzles and challenges. Nerds like me,
in other words...:-)
Bill Venables.
-----Original Message-----
From: ripley@stats.ox.ac.uk [mailto:ripley@stats.ox.ac.uk]
Sent: Monday, October 28, 2002 5:45 PM
To: Nick.Ellis@csiro.au
Cc: s-news@wubios.wustl.edu
Subject: Re: [S] indexing feature (WAS indexing within a list using
Splus
I think that is cart-before-horse. It is not implemented in R, and there
was a request (nay, a bug report, PR#1558, by one of your colleagues) on
this. It just does not occur in any of the commonly-used S library
sections which have been ported to R.
I surmised at that time that people have not found it useful. I never
have. It must take a certain type of problem (or mindset) to work with
lists of lists of lists.
Brian
On Mon, 28 Oct 2002 Nick.Ellis@csiro.au wrote:
> I got one reply on this indexing feature from Bill Venables. He pointed
out
> that this form of indexing does not occur in R. That may explain why it is
> rarely used, as one would try to avoid incompatibilities between the two
> flavours of S.
>
> Splus> list(list(list(1)))[[c(1,1,1)]]
> [1] 1
>
> R> list(list(list(1)))[[c(1,1,1)]]
> Error: attempt to select more than one element
>
> Nick Ellis
> CSIRO Marine Research mailto:Nick.Ellis@csiro.au
> PO Box 120 ph +61 (07) 3826 7260
> Cleveland QLD 4163 fax +61 (07) 3826 7222
> Australia http://www.marine.csiro.au
>
> > -----Original Message-----
> > From: Nick.Ellis@csiro.au [mailto:Nick.Ellis@csiro.au]
> > Sent: Thursday, October 24, 2002 10:49 AM
> > To: s.su@qut.edu.au
> > Cc: s-news@lists.biostat.wustl.edu
> > Subject: Re: [S] indexing within a list using Splus 2000 and Splus 6
> >
> > For instance
> > A[[c(1,2,3)]] is the same
> > as A[[1]][[2]][[3]].
> >
> > To the s-news community:
> > I don't remember anyone using this form of indexing on
> > s-news. I wonder if
> > anyone routinely uses this kind of indexing, and would like
> > to share any
> > tricks? The feature is not described under help("[["); you
> > have to go to the
> > Programmers' Guide, Chapter 4, section "Subscripting Lists".
--
Brian D. Ripley, ripley@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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