From gmbecker at ucdavis.edu  Thu Sep  8 17:43:09 2016
From: gmbecker at ucdavis.edu (Gabriel Becker)
Date: Thu, 8 Sep 2016 08:43:09 -0700
Subject: [Rd] R (development) changes in arith, logic,
 relop with (0-extent) arrays
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Message-ID: <CADwqtCN2PnTFwsrV-K3=hXt64r5eHYNt5dg0OZZdEcDtPOtJuQ@mail.gmail.com>

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

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