Thank you for such a quick reply, here are some points that I think might have
been missed:
> I would state the question the other way : why are NAs integer indices
> allowed?
> In my experience, they are sometimes useful but they often delay the
> detection of bugs. However, due to backward compatibility, this feature
> cannot be removed. Adding this feature to character indices would worsen the
> problem.
But please also note that character indices with NA are allowed for vectors.
This is more an inconsistency between vectors and matrices. In vectors both
numeric and character sub-setting works with NAs. In matrices only numberic and
not character sub-setting works with NAs. Potentially this in itself can also
be a source of bugs, or, at least surprises.
> Setting names() on a matrix is a rarely used feature that has practically no
> positive and no negative consequences. I see no incentive to change the
> behavior and break existing code.
When writing this message I had the opposite opinion. That this 2nd point is
one of the most bug-probe points of all 3. As I would assume most users setting
names() on a matrix would only do it by accident.
> In my opinion adding these features would improve the consistency of R but
> would add more sources of bugs in an already unsafe language.
I think this maybe is a crux of the thing.
My original impression was that R was “clever” about the usage of NAs by
design. i.e. when you choose an unknown object from a set of objects the result
is an object, but nobody knows which - hence NA. Is it really accepted now that
such a decision was a mistake and lead to bugs in user code?
Kind regards,
Karolis K.
> On May 3, 2023, at 11:15 AM, GILLIBERT, Andre <andre.gillib...@chu-rouen.fr>
> wrote:
>
>
> Karolis wrote:
>> Hello,
>
>> I have stumbled upon a few cases where the behaviour of naming and
>> subsetting in matrices seems unintuitive.
>> All those look related so wanted to put everything in one message.
>
>
>> 1. Why row/col selection by names with NAs is not allowed?
>
>> x <- setNames(1:10, letters[1:10])
>> X <- matrix(x, nrow=2, dimnames = list(letters[1:2], LETTERS[1:5]))
>
>> x[c(1, NA, 3)] # vector: works and adds "NA"
>> x[c("a", NA, "c")] # vector: works and adds "NA"
>> X[,c(1, NA, 3)] # works and selects "NA" column
>> X[,c("A", NA, "C")] # <error>
>
> I would state the question the other way : why are NAs integer indices
> allowed?
> In my experience, they are sometimes useful but they often delay the
> detection of bugs. However, due to backward compatibility, this feature
> cannot be removed. Adding this feature to character indices would worsen the
> problem.
>
> I see another reason to keep the behavior as is currently : character indices
> are most often used with column names in contexts were they are unlikely to
> be NAs except as a consequence of a bug. In other words, I fear that the
> valid-use-case/bug ratio would be quite poor with this feature.
>
>> 2. Should setting names() for a matrix be allowed?
>>
>> names(X) <- paste0("e", 1:length(X))
>> X["e4"] # works
>>
>> # but any operation on a matrix drops the names
>> X <- X[,-1] # all names are gone
>> X["e4"] # <error>
>>
>> Maybe names() should not be allowed on a matrix?
>
> Setting names() on a matrix is a rarely used feature that has practically no
> positive and no negative consequences. I see no incentive to change the
> behavior and break existing code.
>
>> 3. Should selection of non-existent dimension names really be an error?
>>
>> x[22] # works on a vector - gives "NA"
>> X[,22] # <error>
>
> This is very often a bug on vectors and should not have been allowed on
> vectors in the first place... But for backwards compatibility, it is hard to
> remove. Adding this unsafe feature to matrices is a poor idea in my opinion.
>
>> A potential useful use-case is matching a smaller matrix to a larger one:
>
> This is a valid use-case, but in my opinion, it adds more problems than it
> solves.
>
>> These also doesn't seem to be documented in '[', 'names', 'rownames’.
>
> Indeed, the documentation of '[' seems to be unclear on indices out of range.
> It can be improved.
>
>> Interested if there specific reasons for this behaviour, or could these
>> potentially be adjusted?
>
> In my opinion adding these features would improve the consistency of R but
> would add more sources of bugs in an already unsafe language.
>
> Sincerely
> André GILLIBERT
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