[R] Object attributes in R

[Henrik Bengtsson]

On 10/11/06, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> You can define your own class then define [ to act any way you would like:
>
> "[.myobj" <- function(x, ...) {
>         y <- unclass(x)[...]

Careful, this is not the same as

           y <- NextMethod("[", x, ...)

/Henrik

>         attributes(y) <- attributes(x)
>         y
> }
>
> tm <- structure(1:10, units = "sec", class = "myobj")
> tm
> tm[3:4] # still has attributes
>
>
>
> On 10/11/06, Michael Toews <mwtoews at ucalgary.ca> wrote:
> > Hi,
> > I have questions about object attributes, and how they are handled when
> > subsetted. My examples will use:
> > tm <- (1:10)/10
> > ds <- (1:10)^2
> > attr(tm,"units") <- "sec"
> > attr(ds,"units") <- "cm"
> > dat <- data.frame(tm=tm,ds=ds)
> > attr(dat,"id") <- "test1"
> >
> > When a "primitive class" object (numeric, character, etc.) is subsetted,
> > the attributes are often stripped away, but the rules change for more
> > complex classes, such as a data.frame, where they 'stick' for the
> > data.frame, but attributes from the members are lost:
> > tm[3:5]        # lost
> > ds[-3]         # lost
> > str(dat[1:3,]) # only kept for data.frame
> >
> > Is there any way of keeping the attributes when subsetted from primitive
> > classes, like a fictional "attr.drop" option within the "[" braces? The
> > best alternative I have found is to make a new object, and copy the
> > attributes:
> > tm2 <- tm[3:5]
> > attributes(tm2) <- attributes(tm)
> >
> > However, for the data.frame, how can I copy the attributes over (without
> > using a for loop -- I've tried a few things using sapply but no success)?
> > Also I don't see how this is consistent with an empty index, "[]", where
> > attributes are always retained (as documented):
> > tm[]
> >
> > I have other concerns about the evaluation of objects with attributes
> > (e.g. ds/tm), where the attributes from the first object are retained
> > for the output, but this evaluation of logic is a whole other can of
> > worms I'd rather keep closed for now.
> >
> > +mt
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch 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 stat.math.ethz.ch 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.
>