Well, that's not very comforting, Duncan. It's like saying that you have to read the engineering specs to drive the car successfully.
I am certainly ignorant of the internals, but I honestly believe well-written documentation on these points would help. I learned a lot when I read V&R's "S Programming" some years ago, so I think that's an existence theorem. Unfortunately, writing such documentation is hard, maybe harder than writing the code even (my own experience documenting my own code). And your logical response -- "Bert, R is open source and would welcome your efforts" -- is not going to get much traction. Like you, I don't have the time (nor, in my case, the smarts). Nevertheless, I agree with Robert's sentiment that it could be done. In particular, plotmath docs really should expand their explanation of appropriate syntax, imho. As always, I end by acknowledging the extraordinary efforts of R's developers. Your success is what has led to such carping. A response of "Aw shaddup" would therefore not be out of line. Best, Bert On Sun, May 20, 2012 at 5:00 PM, Duncan Murdoch <murdoch.dun...@gmail.com> wrote: > On 12-05-20 6:53 PM, Robert Baer wrote: >> >> -----Original Message----- >> From: William Dunlap >> Sent: Saturday, May 19, 2012 11:07 AM >> To: Rolf Turner >> Cc: r-help >> Subject: Re: [R] Names of Greek letters stored as character >> strings;plotmath. >> >> parse(text=paste(...)) works in simple cases but not in others. The >> fortune about it is there because it is tempting to use but if you bury it >> in a general purpose function it will cause problems when people >> start using nonstandard names for variables. bquote(), substitute(), >> call(), and relatives work in all cases. E.g., >> >> > par(mfrow=c(2,1)) >> > power<- "gamma" ; x<- "Waist" ; y<- "Weight" # valid R variable names >> > plot(0, main=bquote(.(as.name(x))^.(as.name(power))/.(as.name(y)))) >> > plot(0, main=parse(text=paste0(x, "^", power, "/", y))) # same as >> previous >> > >> > power<- "gamma" ; x<- "Waist Size (cm)" ; y<- "Weight (kg)" # invalid >> R names >> > plot(0, main=bquote(.(as.name(x))^.(as.name(power))/.(as.name(y)))) >> > plot(0, main=parse(text=paste0(x, "^", power, "/", y))) # whoops >> Error in parse(text = paste0(x, "^", power, "/", y)) : >> <text>:1:7: unexpected symbol >> 1: Waist Size >> ^ >> >> Now you might say that serves me right for using weird variable names, >> but some of us use R as a back end to a GUI system (one not designed >> around R) and don't want to inflict on users R's rules for names when >> we do not have to. >> >> Bill Dunlap >> Spotfire, TIBCO Software >> wdunlap tibco.com >> >> >>> -----Original Message----- >>> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] >>> On Behalf >>> Of Bert Gunter >>> Sent: Saturday, May 19, 2012 7:24 AM >>> To: Gabor Grothendieck >>> Cc: r-help >>> Subject: Re: [R] Names of Greek letters stored as character strings; >>> plotmath. >>> >>> ... and here is another incantation that may be informative. >>> >>> xnm<- as.name("gamma') ## This does the parsing >>> plot(0, xlab =bquote(.(xnm)) >>> >>> The initial puzzle is that if you just set >>> xnm<- "gamma" >>> >>> bquote will insert the string "gamma" rather than the symbol. After >>> all, that's what plotmath sees for xnm. So the key is telling plotmath >>> that it's a symbol, not a string. This can either be done before, as >>> above, or inline, as you and Gabor showed. Unsurprisingly. this also >>> does it, since as.name() is doing the parsing: >>> >>> xnm<- "gamma" >>> plot(0,xlab=bquote(.(as.name(xnm)))) >>> >>> AND we are adhering to Thomas's dictum: bquote is a wrapper for >>> substitute(), which is what he recommends as the preferable >>> alternative to eval(parse(...)) . But, heck -- all such software >>> principles are just guidelines. Whatever works (robustly). >>> >>> HTH. >>> >>> Cheers, >>> Bert >>> >>> On Sat, May 19, 2012 at 3:17 AM, Gabor Grothendieck >>> <ggrothendi...@gmail.com> wrote: >>>> >>>> On Sat, May 19, 2012 at 1:18 AM, Rolf Turner<rolf.tur...@xtra.co.nz> >>>> wrote: >>>>> >>>>> >>>>> I had such good luck with my previous question to r-help, (a few >>>>> minutes >>>>> ago) that I thought I would try again with the following query: >>>>> >>>>>> Suppose I have >>>>>> >>>>>> xNm<- "gamma" >>>>>> >>>>>> I would like to be able to do >>>>>> >>>>>> plot(1:10,xlab =<something involving xNm">) >>>>>> >>>>>> and get the x axis label to be the Greek letter gamma >>>>>> (rather than the literal text string "gamma"). >>>>>> >>>>>> Is this possible? I've messed around with substitute() >>>>>> and bquote() and got nowhere. >>>>> >>>>> >>>>> >>>>> Then, just before clicking on "Send", I had one more thimk, and blow >>>>> me down, I got something that worked: >>>>> >>>>> plot(1:10,xlab=eval(expression(parse(text=xNm)))) >>>>> >>>> >>>> That can be shortened to: >>>> >>>> plot(0, xlab = parse(text = xNm)) >> >> >> >> -- snip -- >> >> >> This discussion has been exceedingly helpful, sort of. >> >> Every time I try to do a task involving this I read the documentation for >> bquote(), expression(), plotmath(), etc., over and over, and I still fail >> to get the big picture of how R parses things under the hood. Typically, >> I >> only succeed each time by frustrating trial and error. Can I ask how you >> guys got a handle on the bigger (besides your usual brilliance<G>)? >> >> Is there more comprehensive documentation in the developer literature or >> is >> there a user wiki that you would recommend for those who never quite get >> the >> big picture? If not, this would be a worthy topic for an R Journal >> article >> if someone has knowledge and the time to do it. Wish I were knowledgeable >> enough to do it myself. > > > I think you have to try writing C code to work with R objects to really > understand what's going on. Reading those sections of the Writing R > Extensions manual will probably help, but actually writing C code to do it > may be necessary. > > It's not really a very complicated system, it's just that things that are > obviously different in C (e.g. the R symbol name "gamma" versus the string > "gamma") look confusingly similar in R. > > You might be able to figure this out by studying the result of str(x) (or > the low level .Internal(inspect(x))) for lots of different x objects, but I > don't think it's going to make sense unless you know what's going on behind > the curtain. > > Duncan Murdoch > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
