[Rd] class(<matrix>) |--> c("matrix", "arrary") [was "head.matrix ..."]

[Pages, Herve]

On 11/14/19 05:47, Hadley Wickham wrote:
> On Sun, Nov 10, 2019 at 2:37 AM Martin Maechler
> <maechler using stat.math.ethz.ch> wrote:
>>
>>>>>>> Gabriel Becker
>>>>>>>      on Sat, 2 Nov 2019 12:37:08 -0700 writes:
>>
>>      > I agree that we can be careful and narrow and still see a
>>      > nice improvement in behavior. While Herve's point is valid
>>      > and I understand his frustration, I think staying within
>>      > the matrix vs c(matrix, array) space is the right scope
>>      > for this work in terms of fiddling with inheritance.
>>
>>   [.................]
>>
>>
>>>> Also, we seem to have a rule that inherits(x, c)  iff  c %in% class(x),
>>>
>>> good point, and that's why my usage of  inherits(.,.) was not
>>> quite to the point.  [OTOH, it was to the point, as indeed from
>>>        the ?class / ?inherits docu, S3 method dispatch and inherits
>>>        must be consistent ]
>>>
>>>      > which would break -- unless we change class(x) to return the whole
>>> set of inherited classes, which I sense that we'd rather not do....
>>
>>    [................]
>>
>>> Note again that both "matrix" and "array" are special [see ?class] as
>>> being of  __implicit class__  and I am considering that this
>>> implicit class behavior for these two should be slightly
>>> changed ....
>>>
>>> And indeed I think you are right on spot and this would mean
>>> that indeed the implicit class
>>> "matrix" should rather become c("matrix", "array").
>>
>> I've made up my mind (and not been contradicted by my fellow R
>> corers) to try go there for  R 4.0.0   next April.
> 
> I can't seem to find the previous thread, so would you mind being a
> bit more explicit here? Do you mean adding "array" to the implicit
> class?

It's late in Europe ;-)

That's my understanding. I think the plan is to have class(matrix()) 
return c("matrix", "array"). No class attributes added to matrix or 
array objects.

It's all what is needed to have inherits(matrix(), "array") return TRUE 
(instead of FALSE at the moment) and S3 dispatch pick up the foo.array 
method when foo(matrix()) is called and there is no foo.matrix method.

> Or adding it to the explicit class? Or adding it to inherits?
> i.e. which of the following results are you proposing to change?
> 
> is_array <- function(x) UseMethod("is_array")
> is_array.array <- function(x) TRUE
> is_array.default <- function(x) FALSE
> 
> x <- matrix()
> is_array(x)
> #> [1] FALSE
> x <- matrix()
> inherits(x, "array")
> #> [1] FALSE
> class(x)
> #> [1] "matrix"
> 
> It would be nice to make sure this is consistent with the behaviour of
> integers, which have an implicit parent class of numeric:

I agree but I don't know if Martin wants to go that far for R 4.0. 
Hopefully that's the longer term plan though (maybe for R 4.1?).
Note that there are other situations that could follow e.g. 
data.frame/list and probably more...

H.


> 
> is_numeric <- function(x) UseMethod("is_numeric")
> is_numeric.numeric <- function(x) TRUE
> is_numeric.default <- function(x) FALSE
> 
> x <- 1L
> is_numeric(x)
> #> [1] TRUE
> inherits(x, "numeric")
> #> [1] FALSE
> class(x)
> #> [1] "integer"
> 
> Hadley
> 

-- 
Hervé Pagès

Program in Computational Biology
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