R help - May 2013 - attr vs attributes

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]]

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


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]]
>
> ______________________________________________
> 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.
>