[Rd] all.equal.list() sometimes fails with unnamed and named components (PR#674)

Kurt Hornik Kurt.Hornik@ci.tuwien.ac.at
Wed, 4 Oct 2000 08:25:12 +0200 (CEST)

>>>>> Prof Brian Ripley writes:

>> To: Kurt.Hornik@ci.tuwien.ac.at
>> Cc: cberry@tajo.ucsd.edu, r-devel@stat.math.ethz.ch
>> Subject: Re: [Rd] all.equal.list() sometimes fails with unnamed and named 
> components (PR#674)
>> From: Peter Dalgaard BSA <p.dalgaard@biostat.ku.dk>
>> Date: 03 Oct 2000 18:05:50 +0200
>> Kurt Hornik <Kurt.Hornik@ci.tuwien.ac.at> writes:
>> > Maybe we should change this as follows: if either of the two lists has
>> > names, work though the named components.  Warn about the ones not
>> > present in both.  Compare the ones present in both.  Then get rid of all
>> > named components and compare what is left in positional order.
>> > 
>> > As I said, I am not sure that this is really what we want.
>> > 
>> > Comments?
>> I think you might be right, and also that this is an easy thing to
>> implement. Then we'd have
>> all.equal(list(a=1,b=2,3,4),list(3,b=2,4,a=1)) == TRUE
>> Right?

> Probably not. Lists do have orderings: they are not sets but generic
> vectors.

>> However, BigBrother has
>> > all.equal(list(a=1,b=2,3,4),list(3,b=2,4,a=1)) 
>> [1] "Names: 2 string mismatches"
>> attr(, "continue"):
>> [1] T
>> > all.equal(list(a=1,b=2,3,4), list(a=1,b=2,4,3))
>> [1] T

> That's not what current versions of S-PLUS give, as one might hope.

>> ..which does look like a "compatible bug"
>> Hmm. Maybe one wants positional matching in any case? But then, what
>> is the named-component extraction about??

> I think that both the names and components should match exactly (the
> components recursively).  Unfortunately the named-component extraction
> is partial matching (at least, sometimes) so the ordering of the names
> always matters.  (There's an S/R difference here I keep forgetting to 
> write down. I think it is 

> x <- list(aa=1, bb=2)
> x["a"]

> which gives in S
> $aa:
> [1] 1
> and in R
> $"NA"
> so S always partial matches, but R does not always.)

More precisely, we have

R> x[["a"]]
[1] 1
R> x["a"] 

Does this make sense at all?  Comparing it to

R> x <- list(aa=1, bb=2, "NA"=3)
R> x["NA"]
[1] 3

I would think that the x["a"] incorrectly indicates that the list has a
named component "NA" with value NULL ...

What should we do about all.equal.list()?  Should we deal with the named
components first and strip them off, or always go the positional route?
Your comment that lists are generic vectors would indicate that the
second approach is more appropriate ...

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