This may be a profoundly bad idea, but if deduction is beyond the skill of those with time, perhaps an inferential approach could be used. Create examples of when one approach versus another works. A book of spells, if you will, so that rather than hoping and typing wildly, the magic incantation can simply be looked up.
Josh On May 20, 2012, at 19:28, Bert Gunter <gunter.ber...@gene.com> wrote: > 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. ______________________________________________ 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.
