thanks, both.
the only real difference between the two approaches that i can see is when
assigning _new_ attributes to an object where the attribute name is itself
variable.
something like this:
> attributes(my_obj)[[my_attr_name]] <- my_attr_value
...fails when my_obj doesn't already have an attribute named my_attr_name.
BUT(!) it does work just fine when the attribute named my_attr_name is
already attached to my_obj.
i guess in the end attr(...) is just easier, but i can also see a spot of
confusion in the 'attributes(x)[[y]] <- z' working sometimes for folks and
sometimes not.
(to be clear, it's pretty easy to figure out when it does and doesn't work,
but if there's a new programmer coming along and it works the first time,
when the upstream code changes a bit (i.e. the attribute name changes) and
this attribute-setting line then fails, it could be very confusing :-)
thanks for the thoughts!
cheers,
-m
On Fri, May 10, 2013 at 10:58 AM, Duncan Murdoch
<murdoch.dun...@gmail.com>wrote:
> 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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>> > PLEASE do read the posting guide http://www.R-project.org/**
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>> >
>>
>> ______________________________**________________
>> R-help@r-project.org mailing list
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>> PLEASE do read the posting guide http://www.R-project.org/**
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>>
>
>
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