Re: [R] Rule for accessing attributes?

From: Tribo Laboy <tribolaboy_at_gmail.com>
Date: Thu, 27 Mar 2008 16:30:54 +0900

So am I to understand that the only realy _correct_ and _recommended_ way of accessing the attributes is through

attr(someobject, "attributename") ?

Regards,

TL

On Thu, Mar 27, 2008 at 4:16 PM, Prof Brian Ripley <ripley_at_stats.ox.ac.uk> wrote:
> 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
>



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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 - 07:33:39 GMT

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