[Rd] replicating lists
Prof Brian Ripley
Thu, 12 Apr 2001 09:40:43 +0100 (BST)
On Thu, 12 Apr 2001, Jonathan Rougier wrote:
> Hi Brian,
> After a discussion with David James can you clarify exactly what you think
> the behaviour of "rep" will be? The three alternatives for rep(fred, 5)
> would appear to be
> > fred <- list(happy = 1:10, name = "squash")
> > list(fred)[rep(1, 5)] # version 1
> > fred[rep(seq(along=fred), length=5)] # version 2
> > unlist(list(fred)[rep(1, 5)], recursive=FALSE) # version 3
> I was expecting the first, as this makes sense in the context of
> > tmp <- array(fred, c(3, 4))
> but I can see that the second is also a natural way to think about
> replicating a list. I also notice that S+ uses version 3. Personally I
> don't like version 3 as it is going to duplicate names, and it is not
> going to fit with "array".
> Confused, Jonathan.
We follow the prototype in cases of doubt, so version 3. *However*,
S-PLUS does different things by version, so version 6.0 drops the
duplicated names. I really think only 3 makes sense: a list is a generic
vector, and you do exactly the same thing as for any other sort of vector.
The only issue is the names, and
x <- letters[1:3]
names(x) <- x
drops names in S+6.0, keeps them in S+3.4 and R. So the S-PLUS versions
are doing consistent things with character vectors and lists.
As for array, again it fits with all other sorts of vectors. I think you
are misconceiving what a list is: think of it as a vector with
components of different types. An array list is just an array with
elements of different types. The problems you had with [[1, ]] stem from
the same problem,
Brian D. Ripley, firstname.lastname@example.org
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 272860 (secr)
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