[Rd] replicating lists
Thu, 12 Apr 2001 12:58:45 +0200
>>>>> Prof Brian Ripley writes:
> 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
> rep(x, 5)
> 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.
We had a similar discussion when fixing all.equal problems with lists.
These are generic vectors and not hashtables, hence I think the above is
the ``right approach'' (following the general principle).
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