From wdunlap at tibco.com  Thu Sep  8 19:05:33 2016
From: wdunlap at tibco.com (William Dunlap)
Date: Thu, 8 Sep 2016 10:05:33 -0700
Subject: [Rd] R (development) changes in arith, logic,
 relop with (0-extent) arrays
In-Reply-To: <CADwqtCN2PnTFwsrV-K3=hXt64r5eHYNt5dg0OZZdEcDtPOtJuQ@mail.gmail.com>
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	<22474.35836.489860.992765@aragorn.wu.ac.at>
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	<22477.32999.558832.601073@stat.math.ethz.ch>
	<22479.9847.747220.924128@stat.math.ethz.ch>
	<22479.58007.358121.626142@stat.math.ethz.ch>
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	<22481.16979.861309.264630@stat.math.ethz.ch>
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Message-ID: <CAF8bMcYBMduLcp_aQoTh74MBBKB9QnTDQG9J_dZyTrFkGd0azw@mail.gmail.com>

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.

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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[Rd] R (development) changes in arith, logic, relop with (0-extent) arrays
William Dunlap