[Rd] R (development) changes in arith, logic, relop with (0-extent) arrays
robin hankin
hankin.robin at gmail.com
Thu Sep 8 00:05:21 CEST 2016
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.
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]]
More information about the R-devel
mailing list