BDR failed to mention that his and Venables's book, S PROGRAMMING, is an excellent reference on many of these language issues (helped me a lot, anyway)even though, by now, some of it may be a bit dated.
Bert Gunter Genentech Nonclinical Statistics -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of baptiste Auguié Sent: Thursday, June 26, 2008 5:54 AM To: R Help Subject: Re: [R] expression, strsplit, ... OK, thanks to both of you for the clarifications. I guess part of my confusion came from the numerous functions and concepts involved in producing such labels: - call vs string vs formula vs expression ... - substitute, bquote, expression, "~", .(), ... I take it as a good thing once you have some experience, as it probably gives several ways to cat a string. The "expense of clarity" in the use of "~" was useful for me complaining about the rather verbose syntax of some plotmath examples. I may try to produce some examples in the future for the R wiki to illustrate these particular annotation details. Thanks again, Baptiste On 26 Jun 2008, at 12:07, Prof Brian Ripley wrote: > On Thu, 26 Jun 2008, baptiste Auguié wrote: > >> >> On 25 Jun 2008, at 19:45, Gabor Grothendieck wrote: >> >>> Try this: >>> plot(1, xlab = ~ alpha / V * m^-3 * kg ^-2 * l^4) >> >> >> Thanks, I would never have expected this code to work, this is a >> mystery to me! Actually, I thought xlab wanted an expression, but >> it seems to be happy with a formula. > > From ?plotmath > > In most cases other language objects (names and calls) are > coerced > to expressions and so can also be used. > > A formula is a call: > >> mode(~ alpha / V * m^-3 * kg ^-2 * l^4) > [1] "call" > > That was just GG saving himself a few key strokes at the expense of > clarity: > > plot(1, xlab = expression(alpha / V * m^-3 * kg ^-2 * l^4)) > > is what this is coerced to. > > >> Also, the handling of exponents is cleverer than I naively assumed. > > It is exactly as documented. > >> I think an example like the one above would make a nice addition >> to the plotmath documentation. > > I don't see what it adds to those already there. > >> >> One small thing bothers me: can one use a similar syntax and use >> something like bquote to substitute a variable? > > You use substitute() to do that: > >> substitute(alpha * aaa / V * m^-3 * kg ^-2 * l^4, list(aaa=a)) > alpha * " some text "/V * m^-3 * kg^-2 * l^4 > >> say, >> >> a <- " some text " >> >>> plot(1, xlab = ~ alpha * `a` / V * m^-3 * kg ^-2 * l^4) >> >> to produce, >> >> >>> plot(1, xlab = ~ alpha * " some text " / V * m^-3 * kg ^-2 * l^4) >> >> but I can't get either bquote, deparse, substitute, "``" to >> produce the desired substitution in this formula. > > You can't 'substitute' in a formula, but you can in the RHS of a > formula, form[[2]] in your case. > >> Many thanks, >> >> baptiste >> >> >> >> >>> On Wed, Jun 25, 2008 at 1:06 PM, baptiste Auguié >>> <[EMAIL PROTECTED]> wrote: >>>> DeaR list, >>>> I'm a bit lost in the behavior of substitute and co. >>>> I often use fairly long axis labels in my graphs (long to write, >>>> that is). >>>> Typically, they would contain some greek letters and units with >>>> exponents, >>>> as in: >>>> >>>>> xlab=expression(paste("text ", alpha, " / ", V,".", m^ >>>>> {-3}, ".", >>>>> kg^{-2}, ".", l^{4})) >>>> To make this a bit prettier, I've attempted to mimic the >>>> behavior of the >>>> SIstyle latex package which defines a macro that cleverly parses an >>>> expression for units, exponents, etc. My code fails in putting >>>> together the >>>> unit, as seen in the example below: >>>>> makeUnits <- function(expr){ # formats the units >>>>> units.list <- strsplit(expr, "[[:blank:]]", perl=F) >>>>> expr.list <- strsplit(unlist(units.list), "\\^", perl=T) >>>>> units <- unlist(lapply(expr.list, function(unit) { >>>>> if (length(unit) == 2) >>>>> paste(unit[1],"^{",unit[2],"}",sep="") >>>>> else paste(unit,sep="") >>>>> })) >>>>> cat(units, sep=".") >>>>> } >>>>> expr <- "V m^-3 kg^-2 l^4" >>>>> makeUnits(expr) # this works, and produces: >>>> # V.m^{-3}.kg^{-2}.l^{4} >>>>> silab <- function(..., units=NULL){ # creates a valid >>>>> expression for xlab >>>>> and co. >>>>> dotCalls <- substitute(list(...)) >>>>> nArgs <- length(dotCalls) >>>>> if (!is.null(units)) myUnits <- makeUnits(units) >>>>> if (!is.null(units)) return(substitute(paste(..., " / ", >>>>> myUnits))) >>>>> if (is.null(units)) return(substitute(paste(...))) >>>>> } >>>>> silab("text", alpha, units = "V m^-3 kg^-2 l^4") # the result is >>>>> obviously not what I want >>>>> par(mfrow=c(2, 1)) # comparison of the desired output and the >>>>> current one >>>>> plot(1:10, 1:10, >>>>> xlab=silab("text ", alpha, units = "V m^-3 kg^-2 l^4"), >>>>> ylab=silab("simple text")) >>>>> plot(1:10, 1:10, >>>>> xlab=expression(paste("text ", alpha, " / ", V,".", m^ >>>>> {-3}, ".", >>>>> kg^{-2}, ".", l^{4})), >>>>> ylab="simple text") >>>> Any thoughts welcome! >>>> Sincerely, >>>> baptiste >>>> _____________________________ >>>> Baptiste Auguié >>>> Physics Department >>>> University of Exeter >>>> Stocker Road, >>>> Exeter, Devon, >>>> EX4 4QL, UK >>>> Phone: +44 1392 264187 >>>> http://newton.ex.ac.uk/research/emag >>>> http://projects.ex.ac.uk/atto >>>> ______________________________________________ >>>> 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. >> >> _____________________________ >> >> Baptiste Auguié >> >> Physics Department >> University of Exeter >> Stocker Road, >> Exeter, Devon, >> EX4 4QL, UK >> >> Phone: +44 1392 264187 >> >> http://newton.ex.ac.uk/research/emag >> http://projects.ex.ac.uk/atto >> >> ______________________________________________ >> 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. > > -- > Brian D. Ripley, [EMAIL PROTECTED] > Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ > University of Oxford, Tel: +44 1865 272861 (self) > 1 South Parks Road, +44 1865 272866 (PA) > Oxford OX1 3TG, UK Fax: +44 1865 272595 _____________________________ Baptiste Auguié Physics Department University of Exeter Stocker Road, Exeter, Devon, EX4 4QL, UK Phone: +44 1392 264187 http://newton.ex.ac.uk/research/emag http://projects.ex.ac.uk/atto ______________________________________________ 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.
