[R] $ operator is invalid for atomic vectors, returning NULL - what is the right thing to do then?
Prof Brian Ripley
ripley at stats.ox.ac.uk
Thu Dec 6 13:22:39 CET 2007
On Thu, 6 Dec 2007, Søren Højsgaard wrote:
> Dear all,
> Starting from a recent version of R,
>From R 2.5.0, not so recent.
> the $ became "unusable" on atomic vectors, e.g.
>> x <- c(a=1,b=2)
>> x$a
> NULL
> Warning message:
> In x$a : $ operator is invalid for atomic vectors, returning NULL
> I can of course do
>> x['a']
> - but that requires more typing (5 characters rather than 2).
>
> Apologies if I've missed a an announcement regarding this, but
> 1) Is there an alternative to the ['a'] and
> 2) Why was this change made?
It has always returned NULL on atomic vectors: see the help page.
E.g. in R 2.0.0 from 2004:
> x <- c(a=1,b=2)
> x$a
NULL
> x['a']
a
1
The warning was added three versions of R ago: the announcement is in the
NEWS file for 2.5.0.
USER-VISIBLE CHANGES
o Using $ on an atomic vector now raises a warning, as does use
on an S4 class for which a method has not been defined.
I think you have exemplified the answer to your question '2)': because
users misunderstood what it did.
In R 2.7.0 this will be an error, since package programmers did not seem
to be heeding the warnings.
--
Brian D. Ripley, ripley at 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 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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