(PR#1558) [Rd] language: bug or feature: vector-subscript of

[ripley@stats.ox.ac.uk]

On Wed, 15 May 2002 mark.bravington@csiro.au wrote:

> Full_Name: Mark Bravington
> Version: R1.3.1 & R1.5.0
> OS: Windows 2000
> Submission from: (NULL) (140.79.2.3)
>
>
> R doesn't like the use of subscripts with length > 1, to get into recursive
> lists:
>
> > listio_ list( a=list( b=9, c='hello'), d=1:5)
> > listio[[ c( 1, 2)]]
> Error: attempt to select more than one element
> >
>
> S is more relaxed:
>
> test>  listio_ list( a=list( b=9, c='hello'), d=1:5)
> test> listio[[ c(1,2)]]
> [1] "hello"
> test>
>
> The same goes for assignment into recursive lists.
>
> I find this feature essential, so I eventually wrote the workarounds below. But
> I'm sure these are slow and ungainly.
>
> Could this feature not be added as a primitive?

[[ is already a primitive, and nowhere that I can see is it documented
that it allows an argument of length 2.  So it is neither a bug nor a
feature, but a difference from S.

If you submit a patch based on the current R-devel sources, we will add it
if it checks out.  Otherwise, as no one else has ever expressed a need of
this feature, it is very unlikely to get implemented.  R is not a clone of
S, and has the features it has because the workers had need of them.

Please do _not_ use "foo_ ".  It is not a meaningful grouping, and it is
planned to deprecate `_' in R shortly.

-- 
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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