From gmbecker at ucdavis.edu  Thu Sep  8 19:22:17 2016
From: gmbecker at ucdavis.edu (Gabriel Becker)
Date: Thu, 8 Sep 2016 10:22:17 -0700
Subject: [Rd] R (development) changes in arith, logic,
 relop with (0-extent) arrays
In-Reply-To: <CAF8bMcYBMduLcp_aQoTh74MBBKB9QnTDQG9J_dZyTrFkGd0azw@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>
	<CAHHjBM6yvrgwOFiFAtM+w8BGmdwn114Z6gfyjMEsLQDLV8mA5A@mail.gmail.com>
	<22481.16979.861309.264630@stat.math.ethz.ch>
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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

	[[alternative HTML version deleted]]



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