>>>>> William Dunlap >>>>> on Fri, 21 Feb 2020 14:05:49 -0800 writes:
> 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$Two[[1]] <- 2 > from the current list(One=1,Two=2) to list(One=1, Two=list(2)) > and the result of > F <- 1L ; levels(F)[[1]] <- "one" > from structure(1L, levels="one") to structure(1L, levels=list("one"))? Yes (twice). This is indeed what happens in current R-devel, as I had committed the proposition above yesterday. So R-devel (with svn rev >= 77844 ) does this : > L <- list(One=1) ; L$Two[[1]] <- 2 ; dput(L) list(One = 1, Two = list(2)) > F <- 1L ; levels(F)[[1]] <- "one" ; dput(F) structure(1L, .Label = list("one")) > but I find that still considerably more logical than current (pre R-devel) R's > L <- list(One=1) ; L$Two[[1]] <- 2 ; dput(L) list(One = 1, Two = 2) > L <- list(One=1) ; L$Two[[1]] <- 2:3 ; dput(L) list(One = 1, Two = list(2:3)) > > F <- 1L ; levels(F)[[1]] <- "one" ; dput(F) structure(1L, .Label = "one") > F <- 1L ; levels(F)[[1]] <- c("one", "TWO") ; dput(F) structure(1L, .Label = list(c("one", "TWO"))) > > 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 don't entirely get what you mean, but) indeed, the [[<- assignments will be closer to corresponding $<- assignments... which I thought would be another good thing about the change. > 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? Well, good question. I'd guess one would get such warnings "all over the place", and if a warning is given only once per session it may not be effective ... also the warning be confusing to the 99.9% of R users who don't even get what we are talking about here ;-) Thank you for your comments.. I did not get too many. Martin > Bill Dunlap > TIBCO Software > wdunlap tibco.com > On Wed, Feb 19, 2020 at 12:59 PM Martin Maechler <maech...@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@r-project.org mailing list >> >> https://stat.ethz.ch/mailman/listinfo/r-devel >> >> > ______________________________________________ >> > R-devel@r-project.org mailing list >> > https://stat.ethz.ch/mailman/listinfo/r-devel >> >> ______________________________________________ >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel