[Rd] head.matrix can return 1000s of columns -- limit to n or add new argument?

[peter dalgaard]

Hmm, the problem I see here is that these implied classes are all inherently one-off. We also have 

> inherits(matrix(1,1,1),"numeric")
[1] FALSE
> is.numeric(matrix(1,1,1))
[1] TRUE
> inherits(1L,"numeric")
[1] FALSE
> is.numeric(1L)
[1] TRUE

and if we start fixing one, we might need to fix all. 

For method dispatch, we do have inheritance, e.g.

> foo.numeric <- function(x) x + 1
> foo <- function(x) UseMethod("foo")
> foo(1)
[1] 2
> foo(1L)
[1] 2
> foo(matrix(1,1,1))
     [,1]
[1,]    2
> foo.integer <- function(x) x + 2
> foo(1)
[1] 2
> foo(1L)
[1] 3
> foo(matrix(1,1,1))
     [,1]
[1,]    2
> foo(matrix(1L,1,1))
     [,1]
[1,]    3

but these are not all automatic: "integer" implies "numeric", but "matrix" does not imply "numeric", much less "integer".

Also, we seem to have a rule that inherits(x, c) iff c %in% class(x), 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....

-pd

> On 30 Oct 2019, at 12:29 , Martin Maechler <maechler using stat.math.ethz.ch> wrote:
> 
> Note however the following  historical quirk :
> 
>> sapply(setNames(,1:5), function(K) inherits(array(pi, dim=1:K), "array"))
>    1     2     3     4     5 
> TRUE FALSE  TRUE  TRUE  TRUE 
> 
> (Is this something we should consider changing for R 4.0.0 -- to
> have it TRUE also for 2d-arrays aka matrix objects ??)

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Office: A 4.23
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