[R] Rule for accessing attributes?

[Prof Brian Ripley]

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