Re: [R] Rule for accessing attributes?

From: Christos Hatzis <christos.hatzis_at_nuverabio.com>
Date: Thu, 27 Mar 2008 09:38:31 -0400

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...

-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?
> >>
> >> ______________________________________________
> >> 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.
> >>
> >>
> >
> > ______________________________________________
> > 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.
>
>



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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. Received on Thu 27 Mar 2008 - 17:45:51 GMT

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