[Rd] R (development) changes in arith, logic, relop with (0-extent) arrays
Gabriel Becker
gmbecker at ucdavis.edu
Thu Sep 8 19:22:17 CEST 2016
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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