Rule for accessing attributes?
On Thu, 27 Mar 2008, Christos Hatzis wrote:
Yes, indeed. The help page says that @ extracts the contents of a slot in S4 objects. But you mention below that this 'works' for S3 objects because S4 slots are stored as attributes. Doesn't this mean that @ is currently implemented to access attributes of objects in general (attributes of S3 objects or slots of S4 objects that are implemented as attributes)? I realize that this might change in the future...
Yes, but it will change, quite possibly for 2.7.0.
-Christos
-----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Prof Brian Ripley Sent: Thursday, March 27, 2008 3:17 AM To: Christos Hatzis Cc: r-help at r-project.org Subject: Re: [R] Rule for accessing attributes? Oh please don't recommend misuse of @ to those already confused. @ is for accessing slots in S4 objects. This 'works' because they happen to be stored as attributes. See the help page (and the warning that it does no checking - we may change that). Similarly, plt$title <- "My Title" works because the package maintainer (of ggplot2, unmentioned?) has chosen to set things up that way. R is very flexible, and there is plenty of scope for package authors to do confusing things. On Thu, 27 Mar 2008, Christos Hatzis wrote:
You need to use the '@' operator to directly access attributes (not elements) of objects:
lst at names
[1] "x" "y" "z" See ?'@' for more details. -Christos
-----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Tribo Laboy Sent: Thursday, March 27, 2008 12:16 AM To: r-help at r-project.org Subject: [R] Rule for accessing attributes? Hi ! I am a new user and quite confused by R-indexing. Make a list and get the attributes lst <- list(x = 1:3, y = 4:6, z = 7:9) attributes(lst) This returns: $names [1] "x" "y" "z" I can easily do: nm <-names(lst) or nm <-attr(lst,"names") which both return the assigned names of the named list
'lst', but why
then this doesn't work: lst$names ? I am confused ... Moreover, I noticed that some of the
objects (e.g.
plot objects returned by ggplot) also have attributes when
queried by
the 'attributes' function, but they are accessible by the
$ notation.
(e.g. xydf <- data.frame(x = 1:5, y = 11:15) plt <- ggplot(data = xydf, aes(x = x,y = y)) + geom_point() attributes(plt) Now we can change the title: plt$title <- "My Title" plt So is it some inconsistency or am I missing something important?
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______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
-- 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
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
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