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

[Kurt Hornik]

>>>>> Prof Brian D Ripley writes:

> On Wed, 4 Oct 2000, Kurt Hornik wrote:
>> > 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"
>> > NULL
>> > so S always partial matches, but R does not always.)
>> 
>> More precisely, we have
>> 
R> x[["a"]]
>> [1] 1
R> x["a"] 
>> $"NA"
>> NULL
>> 
>> Does this make sense at all?  Comparing it to
>> 
R> x <- list(aa=1, bb=2, "NA"=3)
R> x["NA"]
>> $"NA"
>> [1] 3
>> 
>> I would think that the x["a"] incorrectly indicates that the list has a
>> named component "NA" with value NULL ...

> Yes, so would I. I think it is a bug in R.

Agreed.  Should not be too hard to spot ...

>> 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 ...

> See the first two lines I've left here. I think it should be
> positional matching *and* the names should match too. That is,
> all.equal.list would fail if one list had names and other did not.

Well should it really FAIL?

What would be the precendence of the comparisons?  E.g.,

* compare the lenghts.  If different, only retain the components from 1
to the smaller lenght.

* Go through these.  If they have names, compare the names.  Then
compare the values.

[If both components have the same name but differ in value, the output
would display the name and not the position, right?  I mean something
like
  msg <- c(msg, paste("Component ", nc[i], ": ", mi, sep=""))
rather than
  msg <- c(msg, paste("Component ", i, ": ", mi, sep=""))
???]

-k
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