[Rd] R (development) changes in arith, logic, relop with (0-extent) arrays
Paul Gilbert
pgilbert902 at gmail.com
Thu Sep 8 20:00:58 CEST 2016
On 09/08/2016 01:22 PM, Gabriel Becker wrote:
> On Thu, Sep 8, 2016 at 10:05 AM, William Dunlap <wdunlap at tibco.com> wrote:
>
>> Shouldn't binary operators (arithmetic and logical) should throw an error
>> when one operand is NULL (or other type that doesn't make sense)? This is
>> a different case than a zero-length operand of a legitimate type. E.g.,
>> any(x < 0)
>> should return FALSE if x is number-like and length(x)==0 but give an error
>> if x is NULL.
>>
> Bill,
>
> That is a good point. I can see the argument for this in the case that the
> non-zero length is 1. I'm not sure which is better though. If we switch
> any() to all(), things get murky.
>
> Mathematically, all(x<0) is TRUE if x is length 0 (as are all(x==0), and
> all(x>0)), but the likelihood of this being a thought-bug on the author's
> part is exceedingly high, imho.
I suspect there may be more R users than you think that understand and
use vacuously true in code. I don't really like the idea of turning a
perfectly good and properly documented mathematical test into an error
in order to protect against a possible "thought-bug".
Paul
So the desirable behavior seems to depend
> on the angle we look at it from.
>
> My personal opinion is that x < y with length(x)==0 should fail if length(y)
>> 1, at least, and I'd be for it being an error even if y is length 1,
> though I do acknowledge this is more likely (though still quite unlikely
> imho) to be the intended behavior.
>
> ~G
>
>>
>> I.e., I think the type check should be done before the length check.
>>
>>
>> Bill Dunlap
>> TIBCO Software
>> wdunlap tibco.com
>>
>> On Thu, Sep 8, 2016 at 8:43 AM, Gabriel Becker <gmbecker at ucdavis.edu>
>> wrote:
>>
>>> Martin,
>>>
>>> Like Robin and Oliver I think this type of edge-case consistency is
>>> important and that it's fantastic that R-core - and you personally - are
>>> willing to tackle some of these "gotcha" behaviors. "Little" stuff like
>>> this really does combine to go a long way to making R better and better.
>>>
>>> I do wonder a bit about the
>>>
>>> x = 1:2
>>>
>>> y = NULL
>>>
>>> x < y
>>>
>>> case.
>>>
>>> Returning a logical of length 0 is more backwards compatible, but is it
>>> ever what the author actually intended? I have trouble thinking of a case
>>> where that less-than didn't carry an implicit assumption that y was
>>> non-NULL. I can say that in my own code, I've never hit that behavior in
>>> a
>>> case that wasn't an error.
>>>
>>> My vote (unless someone else points out a compelling use for the behavior)
>>> is for the to throw an error. As a developer, I'd rather things like this
>>> break so the bug in my logic is visible, rather than propagating as the
>>> 0-length logical is &'ed or |'ed with other logical vectors, or used to
>>> subset, or (in the case it should be length 1) passed to if() (if throws
>>> an
>>> error now, but the rest would silently "work").
>>>
>>> Best,
>>> ~G
>>>
>>> On Thu, Sep 8, 2016 at 3:49 AM, Martin Maechler <
>>> maechler at stat.math.ethz.ch>
>>> wrote:
>>>
>>>>>>>>> robin hankin <hankin.robin at gmail.com>
>>>>>>>>> on Thu, 8 Sep 2016 10:05:21 +1200 writes:
>>>>
>>>> > Martin I'd like to make a comment; I think that R's
>>>> > behaviour on 'edge' cases like this is an important thing
>>>> > and it's great that you are working on it.
>>>>
>>>> > I make heavy use of zero-extent arrays, chiefly because
>>>> > the dimnames are an efficient and logical way to keep
>>>> > track of certain types of information.
>>>>
>>>> > If I have, for example,
>>>>
>>>> > a <- array(0,c(2,0,2))
>>>> > dimnames(a) <- list(name=c('Mike','Kevin'),
>>>> NULL,item=c("hat","scarf"))
>>>>
>>>>
>>>> > Then in R-3.3.1, 70800 I get
>>>>
>>>> a> 0
>>>> > logical(0)
>>>> >>
>>>>
>>>> > But in 71219 I get
>>>>
>>>> a> 0
>>>> > , , item = hat
>>>>
>>>>
>>>> > name
>>>> > Mike
>>>> > Kevin
>>>>
>>>> > , , item = scarf
>>>>
>>>>
>>>> > name
>>>> > Mike
>>>> > Kevin
>>>>
>>>> > (which is an empty logical array that holds the names of the
>>> people
>>>> and
>>>> > their clothes). I find the behaviour of 71219 very much preferable
>>>> because
>>>> > there is no reason to discard the information in the dimnames.
>>>>
>>>> Thanks a lot, Robin, (and Oliver) !
>>>>
>>>> Yes, the above is such a case where the new behavior makes much sense.
>>>> And this behavior remains identical after the 71222 amendment.
>>>>
>>>> Martin
>>>>
>>>> > Best wishes
>>>> > Robin
>>>>
>>>>
>>>>
>>>>
>>>> > On Wed, Sep 7, 2016 at 9:49 PM, Martin Maechler <
>>>> maechler at stat.math.ethz.ch>
>>>> > wrote:
>>>>
>>>> >> >>>>> Martin Maechler <maechler at stat.math.ethz.ch>
>>>> >> >>>>> on Tue, 6 Sep 2016 22:26:31 +0200 writes:
>>>> >>
>>>> >> > Yesterday, changes to R's development version were committed,
>>>> >> relating
>>>> >> > to arithmetic, logic ('&' and '|') and
>>>> >> > comparison/relational ('<', '==') binary operators
>>>> >> > which in NEWS are described as
>>>> >>
>>>> >> > SIGNIFICANT USER-VISIBLE CHANGES:
>>>> >>
>>>> >> > [.............]
>>>> >>
>>>> >> > • Arithmetic, logic (‘&’, ‘|’) and comparison (aka
>>>> >> > ‘relational’, e.g., ‘<’, ‘==’) operations with arrays now
>>>> >> > behave consistently, notably for arrays of length zero.
>>>> >>
>>>> >> > Arithmetic between length-1 arrays and longer non-arrays had
>>>> >> > silently dropped the array attributes and recycled. This
>>>> >> > now gives a warning and will signal an error in the future,
>>>> >> > as it has always for logic and comparison operations in
>>>> >> > these cases (e.g., compare ‘matrix(1,1) + 2:3’ and
>>>> >> > ‘matrix(1,1) < 2:3’).
>>>> >>
>>>> >> > As the above "visually suggests" one could think of the changes
>>>> >> > falling mainly two groups,
>>>> >> > 1) <0-extent array> (op) <non-array>
>>>> >> > 2) <1-extent array> (arith) <non-array of length != 1>
>>>> >>
>>>> >> > These changes are partly non-back compatible and may break
>>>> >> > existing code. We believe that the internal consistency gained
>>>> >> > from the changes is worth the few places with problems.
>>>> >>
>>>> >> > We expect some package maintainers (10-20, or even more?) need
>>>> >> > to adapt their code.
>>>> >>
>>>> >> > Case '2)' above mainly results in a new warning, e.g.,
>>>> >>
>>>> >> >> matrix(1,1) + 1:2
>>>> >> > [1] 2 3
>>>> >> > Warning message:
>>>> >> > In matrix(1, 1) + 1:2 :
>>>> >> > dropping dim() of array of length one. Will become ERROR
>>>> >> >>
>>>> >>
>>>> >> > whereas '1)' gives errors in cases the result silently was a
>>>> >> > vector of length zero, or also keeps array (dim & dimnames) in
>>>> >> > cases these were silently dropped.
>>>> >>
>>>> >> > The following is a "heavily" commented R script showing (all
>>> ?)
>>>> >> > the important cases with changes :
>>>> >>
>>>> >> > ------------------------------------------------------------
>>>> >> ----------------
>>>> >>
>>>> >> > (m <- cbind(a=1[0], b=2[0]))
>>>> >> > Lm <- m; storage.mode(Lm) <- "logical"
>>>> >> > Im <- m; storage.mode(Im) <- "integer"
>>>> >>
>>>> >> > ## 1. -------------------------
>>>> >> > try( m & NULL ) # in R <= 3.3.x :
>>>> >> > ## Error in m & NULL :
>>>> >> > ## operations are possible only for numeric, logical or
>>> complex
>>>> >> types
>>>> >> > ##
>>>> >> > ## gives 'Lm' in R >= 3.4.0
>>>> >>
>>>> >> > ## 2. -------------------------
>>>> >> > m + 2:3 ## gave numeric(0), now remains matrix identical to m
>>>> >> > Im + 2:3 ## gave integer(0), now remains matrix identical to Im
>>>> >> (integer)
>>>> >>
>>>> >> > m > 1 ## gave logical(0), now remains matrix identical to
>>> Lm
>>>> >> (logical)
>>>> >> > m > 0.1[0] ## ditto
>>>> >> > m > NULL ## ditto
>>>> >>
>>>> >> > ## 3. -------------------------
>>>> >> > mm <- m[,c(1:2,2:1,2)]
>>>> >> > try( m == mm ) ## now gives error "non-conformable arrays",
>>>> >> > ## but gave logical(0) in R <= 3.3.x
>>>> >>
>>>> >> > ## 4. -------------------------
>>>> >> > str( Im + NULL) ## gave "num", now gives "int"
>>>> >>
>>>> >> > ## 5. -------------------------
>>>> >> > ## special case for arithmetic w/ length-1 array
>>>> >> > (m1 <- matrix(1,1,1, dimnames=list("Ro","col")))
>>>> >> > (m2 <- matrix(1,2,1, dimnames=list(c("A","B"),"col")))
>>>> >>
>>>> >> > m1 + 1:2 # -> 2:3 but now with warning to "become ERROR"
>>>> >> > tools::assertError(m1 & 1:2)# ERR: dims [product 1] do not
>>> match
>>>> the
>>>> >> length of object [2]
>>>> >> > tools::assertError(m1 < 1:2)# ERR: (ditto)
>>>> >> > ##
>>>> >> > ## non-0-length arrays combined with {NULL or double() or ...}
>>>> *fail*
>>>> >>
>>>> >> > ### Length-1 arrays: Arithmetic with |vectors| > 1 treated
>>> array
>>>> >> as scalar
>>>> >> > m1 + NULL # gave numeric(0) in R <= 3.3.x --- still, *but* w/
>>>> >> warning to "be ERROR"
>>>> >> > try(m1 > NULL) # gave logical(0) in R <= 3.3.x --- an
>>> *error*
>>>> >> now in R >= 3.4.0
>>>> >> > tools::assertError(m1 & NULL) # gave and gives error
>>>> >> > tools::assertError(m1 | double())# ditto
>>>> >> > ## m2 was slightly different:
>>>> >> > tools::assertError(m2 + NULL)
>>>> >> > tools::assertError(m2 & NULL)
>>>> >> > try(m2 == NULL) ## was logical(0) in R <= 3.3.x; now error as
>>>> above!
>>>> >>
>>>> >> > ------------------------------------------------------------
>>>> >> ----------------
>>>> >>
>>>> >>
>>>> >> > Note that in R's own 'nls' sources, there was one case of
>>>> >> > situation '2)' above, i.e. a 1x1-matrix was used as a
>>> "scalar".
>>>> >>
>>>> >> > In such cases, you should explicitly coerce it to a vector,
>>>> >> > either ("self-explainingly") by as.vector(.), or as I did in
>>>> >> > the nls case by c(.) : The latter is much less
>>>> >> > self-explaining, but nicer to read in mathematical formulae,
>>> and
>>>> >> > currently also more efficient because it is a .Primitive.
>>>> >>
>>>> >> > Please use R-devel with your code, and let us know if you see
>>>> >> > effects that seem adverse.
>>>> >>
>>>> >> I've been slightly surprised (or even "frustrated") by the empty
>>>> >> reaction on our R-devel list to this post.
>>>> >>
>>>> >> I would have expected some critique, may be even some praise,
>>>> >> ... in any case some sign people are "thinking along" (as we say
>>>> >> in German).
>>>> >>
>>>> >> In the mean time, I've actually thought along the one case which
>>>> >> is last above: The <op> (binary operation) between a
>>>> >> non-0-length array and a 0-length vector (and NULL which should
>>>> >> be treated like a 0-length vector):
>>>> >>
>>>> >> R <= 3.3.1 *is* quite inconsistent with these:
>>>> >>
>>>> >>
>>>> >> and my proposal above (implemented in R-devel, since Sep.5) would
>>>> give an
>>>> >> error for all these, but instead, R really could be more lenient
>>>> here:
>>>> >> A 0-length result is ok, and it should *not* inherit the array
>>>> >> (dim, dimnames), since the array is not of length 0. So instead
>>>> >> of the above [for the very last part only!!], we would aim for
>>>> >> the following. These *all* give an error in current R-devel,
>>>> >> with the exception of 'm1 + NULL' which "only" gives a "bad
>>>> >> warning" :
>>>> >>
>>>> >> ------------------------
>>>> >>
>>>> >> m1 <- matrix(1,1)
>>>> >> m2 <- matrix(1,2)
>>>> >>
>>>> >> m1 + NULL # numeric(0) in R <= 3.3.x ---> OK ?!
>>>> >> m1 > NULL # logical(0) in R <= 3.3.x ---> OK ?!
>>>> >> try(m1 & NULL) # ERROR in R <= 3.3.x ---> change to logical(0)
>>>> ?!
>>>> >> try(m1 | double())# ERROR in R <= 3.3.x ---> change to logical(0)
>>>> ?!
>>>> >> ## m2 slightly different:
>>>> >> try(m2 + NULL) # ERROR in R <= 3.3.x ---> change to double(0)
>>> ?!
>>>> >> try(m2 & NULL) # ERROR in R <= 3.3.x ---> change to logical(0)
>>> ?!
>>>> >> m2 == NULL # logical(0) in R <= 3.3.x ---> OK ?!
>>>> >>
>>>> >> ------------------------
>>>> >>
>>>> >> This would be slightly more back-compatible than the currently
>>>> >> implemented proposal. Everything else I said remains true, and
>>>> >> I'm pretty sure most changes needed in packages would remain to
>>> be
>>>> done.
>>>> >>
>>>> >> Opinions ?
>>>> >>
>>>> >>
>>>> >>
>>>> >> > In some case where R-devel now gives an error but did not
>>>> >> > previously, we could contemplate giving another "warning
>>>> >> > .... 'to become ERROR'" if there was too much breakage, though
>>>> >> > I don't expect that.
>>>> >>
>>>> >>
>>>> >> > For the R Core Team,
>>>> >>
>>>> >> > Martin Maechler,
>>>> >> > ETH Zurich
>>>> >>
>>>> >> ______________________________________________
>>>> >> R-devel at r-project.org mailing list
>>>> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>> >>
>>>>
>>>>
>>>>
>>>> > --
>>>> > Robin Hankin
>>>> > Neutral theorist
>>>> > hankin.robin at gmail.com
>>>>
>>>> > [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
>>>> R-devel at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>>
>>>
>>>
>>>
>>> --
>>> Gabriel Becker, PhD
>>> Associate Scientist (Bioinformatics)
>>> Genentech Research
>>>
>>> [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>>
>>
>
>
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