Rule for accessing attributes?
Thanks, this really solved my problem. Actually, I do have a good introduction to R - a book co-authored by some W.N. Venables and some B.D. Ripley, colloquially called 'MASS' is on my desk. I find it really very helpful. Still, as it is a book on statistics, some details on R are only mentioned in passing. I also use some other books and online resources, but obviously will need to delve a bit deeper. One of the reasons I am moving to R is because it has a great user community. I hope I am not abusing it with too many questions. Regards, TL On Thu, Mar 27, 2008 at 5:16 PM, Prof Brian Ripley
<ripley at stats.ox.ac.uk> wrote:
Use [[ ]]. It seems it is time for you to study a good introduction to R. On Thu, 27 Mar 2008, Tribo Laboy wrote:
> Now, how is it that I can access the contents of a named list by
> dynamically computed name?
>
> To go back to my previous example I have a list and I know the names.
> Now I want do something with that named data in a loop.
>
> lst <- list(x = 1:3, y = 4:6, z = 7:9)
> nm <-names(lst)
> nm
> [1] "x" "y" "z"
>
> I can access the list elements by name directly:
>
> lst$x; lst$y; lst$z,
>
> But I want to do
>
> for (k in 1:3) {
> lst$nm[k]
> }
>
> But this doesn't work, basically because
> lst$nm[1] returns a NULL.
>
> So what do I do?
>
> Thanks for helping,
>
> TL
>
>
> On Thu, Mar 27, 2008 at 4:30 PM, Tribo Laboy <tribolaboy at gmail.com> wrote:
>> So am I to understand that the only realy _correct_ and _recommended_ >> way of accessing the attributes is through >> >> attr(someobject, "attributename") ? >> >> >> Regards, >> >> TL >> >> >> >> On Thu, Mar 27, 2008 at 4:16 PM, Prof Brian Ripley >> <ripley at stats.ox.ac.uk> wrote:
>> > Oh please don't recommend misuse of @ to those already confused. >> > >> > @ is for accessing slots in S4 objects. This 'works' because they happen >> > to be stored as attributes. See the help page (and the warning that it >> > does no checking - we may change that). >> > >> > Similarly, >> > >> > plt$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 >> >
>>
>
-- 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