[R] attr vs attributes

[Duncan Murdoch]

On 10/05/2013 10:50 AM, Rui Barradas wrote:
> Hello,
>
> There's at least one example where only the form attr(x, "foo") <- "bar"
> would work, not the other form. If you want to set attributes
> programatically, use the first form, like in the function below. Note
> that the example is artificial.
>
>
> setAttr <- function(x, attrib, value){
> 	attr(x, attrib) <- value
> 	x
> }
>
> x <- 1:4
> setAttr(x, "foo", "bar")
>
>
> You cannot make
>
> attribute(x)$attrib <- value

But

attributes(x)[[attrib]] <- value

would be fine.  I don't know why Murat thought there would be different 
consistency checks; I'd assume the main difference would be that attr() 
would be quicker.  (It does a lot less: attributes(x)[[attrib]] <- value 
essentially does

temp <- attributes(x)
temp[[attrib]] <- value
attributes(x) <- temp

and there are a lot of wasted operations there.)

Duncan Murdoch

>
>
> Hope this helps,
>
> Rui Barradas
>
> Em 09-05-2013 18:35, Murat Tasan escreveu:
> > hi all -- i looked through the R Language Definition document, but couldn't
> > find any particular warning or example that would clarify the best use of
> > attribute setting for R objects.
> >
> > let x be some R object, and i'd like to add attribute "foo" with value
> > "bar".
> >
> > case 1:
> >> attr(x, "foo") <- "bar"
> >
> > case 2:
> >> attributes(x)$foo <- "bar"
> >
> > in both cases, attributes(x) reveals the appropriate setting has taken
> > place.
> > i'm assuming that attr(...) is 'safer' in the sense that perhaps
> > consistency checks are made?
> > (almost like a generic accessor/setter method?)
> > but i also haven't seen any examples where case 2 (above) would bad... is
> > there are trivial such example out there?
> >
> > BTW -- the cause for interest here is when dealing with dendrogram objects,
> > for which much of the useful data are stored as attributes, and where
> > running dendrapply means having to explicitly set attribute values to
> > retain the tree structure in the resulting object.
> >
> > cheers,
> >
> > -m
> >
> > 	[[alternative HTML version deleted]]
> >
> > ______________________________________________
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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.
> >
>
> ______________________________________________
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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.