[Rd] dimnames incoherence?
William Dunlap
wdun|@p @end|ng |rom t|bco@com
Fri Feb 21 23:05:49 CET 2020
If we change the behavior NULL--[[--assignment from
`[[<-`(NULL, 1, "a" ) # gives "a" (*not* a list)
to
`[[<-`(NULL, 1, "a" ) # gives list("a")
then we have more consistency there *and* your bug is fixed too.
Of course, in other situations back-compatibility would be
broken as well.
Would that change the result of
L <- list(One=1) ; L$Two[[1]] <- 2
from the current list(One=1,Two=2) to list(One=1, Two=list(2))
and the result of
F <- 1L ; levels(F)[[1]] <- "one"
from structure(1L, levels="one") to structure(1L, levels=list("one"))?
This change would make L$Name[[1]] <- value act like L$Name$one <- value
in cases when L did not have a component named "Name" and value
had length 1.
I have seen users use [[<- where [<- is more appropriate in cases like
this. Should there be a way to generate warnings about the change in
behavior as you've done with other syntax changes?
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Wed, Feb 19, 2020 at 12:59 PM Martin Maechler <maechler using stat.math.ethz.ch>
wrote:
> >>>>> Martin Maechler
> >>>>> on Wed, 19 Feb 2020 18:06:57 +0100 writes:
>
> >>>>> Serguei Sokol
> >>>>> on Wed, 19 Feb 2020 15:21:21 +0100 writes:
>
> >> Hi,
> >> I was bitten by a little incoherence in dimnames assignment or may
> be I
> >> missed some point.
> >> Here is the case. If I assign row names via dimnames(a)[[1]], when
> >> nrow(a)=1 then an error is thrown. But if I do the same when
> nrow(a) > 1
> >> it's OK. Is one of this case works unexpectedly? Both? Neither?
>
> >> a=as.matrix(1)
> >> dimnames(a)[[1]]="a" # error: 'dimnames' must be a list
>
> >> aa=as.matrix(1:2)
> >> dimnames(aa)[[1]]=c("a", "b") # OK
>
> >> In the second case, dimnames(aa) is not a list (like in the first
> case)
> >> but it works.
> >> I would expect that the both work or neither.
>
> > I agree (even though I'm strongly advising people to use '<-'
> > instead of '=');
> > which in this case helps you get the name of the function really
> > involved: It is `dimnames<-` (which is implemented in C
> > entirely, for matrices and other arrays).
>
> As a matter of fact, I wrote too quickly, the culprit here is
> the `[[<-` function (rather than `dimnames<-`),
> which has a special "inconsistency" feature when used to "add to NULL";
> almost surely inherited from S, but I now think we should
> consider dropping on the occasion of aiming for R 4.0.0 :
>
> It's documented in ?Extract that length 1 `[[.]]`-assignment works
> specially for NULL (and dimnames(.) are NULL here).
>
> Note you need to read and understand one of the tougher sections
> in the official 'R Language Definition' Manual,
> section -- 3.4.4 Subset assignment ---
> i.e.,
>
> https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Subset-assignment
>
> notably this part:
>
> Nesting of complex assignments is evaluated recursively
>
> names(x)[3] <- "Three"
>
> is equivalent to
>
> `*tmp*` <- x
> x <- "names<-"(`*tmp*`, value="[<-"(names(`*tmp*`), 3, value="Three"))
> rm(`*tmp*`)
>
> and then, apply this to our dimnames(a)[[1]] <- "a"
> and so replace
>
> - 'names<-' by 'dimnames<-'
> - '[<-' by '[[<-'
>
> ----------
>
> Here is the rest of my analysis as valid R code
> {this is not new, Peter Dalgaard had explained this 10 or 20
> years ago to a mailing list audience IIRC} :
>
> ## MM: The problematic behavior (bug ?) is in `[[<-`, not in `dimnames<-` :
>
> `[[<-`(NULL, 1, "a" ) # gives "a" (*not* a list)
> `[[<-`(NULL, 1, c("a","b")) # gives list(c("a","b")) !!
>
> ##==> in C code: in subassign.c [ ~/R/D/r-devel/R/src/main/subassign.c ]
> ##==> function (~ 340 lines)
> ## do_subassign2_dflt(SEXP call, SEXP op, SEXP args, SEXP rho)
> ## has
> "
> line svn r. svn auth. c.o.d.e...
> ---- ------ --------- ----------------------------------------------
> 1741 4166 ihaka if (isNull(x)) {
> 1742 45446 ripley if (isNull(y)) {
> 1743 76166 luke UNPROTECT(2); /* args, y */
> 1744 4166 ihaka return x;
> 1745 45446 ripley }
> 1746 35680 murdoch if (length(y) == 1)
> 1747 68094 luke x = allocVector(TYPEOF(y), 0);
> 1748 24954 ripley else
> 1749 68094 luke x = allocVector(VECSXP, 0);
> 1750 1820 ihaka }
> ---- ------ --------- ----------------------------------------------
> "
> ## so clearly, in case the value is of length 1, no list is created .
>
> ## For dimnames<- Replacing NULL by list() should be done in both cases
> , and then things work :
> `[[<-`(list(), 1, "a" ) # gives list( "a" )
> `[[<-`(list(), 1, c("a","b")) # gives list(c("a","b")) !!
>
> ## but the problem here is that `[[<-` at this time in the game
> ## does *not* know that it comes from dimnames<- ....
>
> ---------------
>
> If we change the behavior NULL--[[--assignment from
>
> `[[<-`(NULL, 1, "a" ) # gives "a" (*not* a list)
>
> to
>
> `[[<-`(NULL, 1, "a" ) # gives list("a")
>
>
> then we have more consistency there *and* your bug is fixed too.
> Of course, in other situations back-compatibility would be
> broken as well.
>
> At the moment, I think we (R Core Team) should consider doing
> that here.
>
> Martin
>
>
>
> >> Your thoughts are welcome.
>
> > I think we'd be happy if you report this formally on R's
> > bugzilla - https://bugs.r-project.org/ - as a bug.
>
> --> https://www.r-project.org/bugs.html
>
> >> From reading bugs.html you note that you should ask for
> >> an account there;
> > as I'm one of the people who get such request by e-mail,
> > in this case, I can do it directly (if you confirm you'd
> > want in a private e-mail).
>
> >> Best, Serguei.
>
> >> PS the same apply for dimnames(a)[[2]]<-.
>
> > (of course)
>
> > NB *and* importantly, the buglet is still in current
> > versions of R
>
> > Best, Martin
>
> >>> sessionInfo()
> >> R version 3.6.1 (2019-07-05) Platform:
> >> x86_64-pc-linux-gnu (64-bit) Running under: Mageia 7
>
> >> Matrix products: default BLAS/LAPACK:
> >> /home/opt/OpenBLAS/lib/libopenblas_sandybridge-r0.3.6.so
>
> >> locale: [1] LC_CTYPE=fr_FR.UTF-8 LC_NUMERIC=C [3]
> >> LC_TIME=fr_FR.UTF-8 LC_COLLATE=fr_FR.UTF-8 [5]
> >> LC_MONETARY=fr_FR.UTF-8 LC_MESSAGES=fr_FR.UTF-8 [7]
> >> LC_PAPER=fr_FR.UTF-8 LC_NAME=C [9]
> >> LC_ADDRESS=C LC_TELEPHONE=C [11]
> >> LC_MEASUREMENT=fr_FR.UTF-8 LC_IDENTIFICATION=C
>
> >> attached base packages: [1] parallel stats graphics
> >> grDevices utils datasets methods [8] base
>
> >> other attached packages: [1] multbxxc_1.0.1
> >> rmumps_5.2.1-11 [3] arrApply_2.1
> >> RcppArmadillo_0.9.800.4.0 [5] Rcpp_1.0.3
> >> slam_0.1-47 [7] nnls_1.4
>
> >> loaded via a namespace (and not attached): [1]
> >> compiler_3.6.1 tools_3.6.1 codetools_0.2-16
>
> >> ______________________________________________
> >> R-devel using r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> > ______________________________________________
> > R-devel using r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
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>
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