[Rd] multiple issues with is.unsorted()

Martin Maechler maechler at stat.math.ethz.ch
Wed Apr 24 17:41:06 CEST 2013

More comments .. see inline

>>>>> Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Wed, 24 Apr 2013 11:29:39 +0200 writes:

    > Dear Herve,
>>>>> Hervé Pagès <hpages at fhcrc.org>
>>>>> on Tue, 23 Apr 2013 23:09:21 -0700 writes:

    >> Hi, In the man page for is.unsorted():

    >> Value:

    >> A length-one logical value.  All objects of length 0 or 1
    >> are sorted: the result will be ‘NA’ for objects of length
    >> 2 or more except for atomic vectors and objects with a
    >> class (where the ‘>=’ or ‘>’ method is used to compare
    >> ‘x[i]’ with ‘x[i-1]’ for ‘i’ in ‘2:length(x)’).

    >> This contains many incorrect statements:

    >>> length(NA)
    >> [1] 1
    >>> is.unsorted(NA)
    >> [1] NA
    >>> length(list(NA))
    >> [1] 1
    >>> is.unsorted(list(NA))
    >> [1] NA

    >> => Contradicts "all objects of length 0 or 1 are sorted".

Ok.  I really think we should change the above.
If NA is for a missing number, it still cannot be unsorted if it
is of length one.

--> the above will give FALSE  "real soon now".

    >>> is.unsorted(raw(2))
    >> Error in is.unsorted(raw(2)) : unimplemented type 'raw'
    >> in 'isUnsorted'

    >> => Doesn't agree with the doc (unless "except for atomic
    >> vectors" means "it might fail for atomic vectors").

Well, the doc says about 'x'
|  \item{x}{an \R object with a class or a numeric, complex, character or
|    logical vector.}
so strictly, is.unsorted() is not to be used on raw vectors.

However I think you have a point:
Raw vectors didn't exist when  is.unsorted()  was
invented, so where not considered back then.
Originally,  raw vectors were really almost only there for
storage, i.e. basically read and write, but now we have
as '<' , '<=' '=='  etc  working well for raw() ,
we could allow  is.unsorted() to work, too.

Note however, that if you try to sort(<raw>) you also always get
an error about sort() not being implemented for raw(),...
something we could arguably reconsider, as we admitted the 
relational operators (< <= == >= >  != ) to work.
{{anyone donating patches to R-devel for sort()ing raw ?}}

    >>> setClass("A", representation(aa="integer")) 
    >>> new("A", aa=4:1) 
    >>> length(a)
    >> [1] 1

    >>> is.unsorted(a)
    >> [1] FALSE
    >>  Warning message: In is.na(x) : is.na() applied
    >> to non-(list or vector) of type 'S4'

    >> => Ok, but it's arguable the warning is useful/justified
    >> from a user point of view. The warning *seems* to suggest
    >> that defining an "is.na" method for my objects is
    >> required for is.unsorted() to work properly but the doc
    >> doesn't make this clear.

you are right.
We are going to improve on this, at least the documentation.


The S4 part I've already started addressing in the last reply.
(and we may get back to that.. )



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