[Rd] R (development) changes in arith, logic, relop with (0-extent) arrays
William Dunlap
wdunlap at tibco.com
Thu Sep 8 19:45:07 CEST 2016
Prior to the mid-1990s, S did "length-0 OP length-n -> rep(NA, n)" and it
was changed
to "length-0 OP length-n -> length-0" to avoid lots of problems like
any(x<0) being NA
when length(x)==0. Yes, people could code defensively by putting lots of
if(length(x)==0)...
in their code, but that is tedious and error-prone and creates really ugly
code.
Is your suggestion to leave the length-0 OP length-1 case as it is but make
length-0 OP length-two-or-higher an error or warning (akin to the length-2
OP length-3 case)?
By the way, the all(numeric(0)<0) is TRUE, as is all(numeric()>0), by de
Morgan's rule, but that is not really relevant here.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Thu, Sep 8, 2016 at 10:22 AM, Gabriel Becker <gmbecker at ucdavis.edu>
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. 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
>>>
>>
>>
>
>
> --
> Gabriel Becker, PhD
> Associate Scientist (Bioinformatics)
> Genentech Research
>
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