On Sat, May 19, 2012 at 2:16 PM, Paul Johnson <pauljoh...@gmail.com> wrote: > On Sat, May 19, 2012 at 11:07 AM, William Dunlap <wdun...@tibco.com> wrote: >> 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 >> > Bill's point is on the money here. We should aim to teach one way that > works always. But finding that one way is the hard part for me. > > Lately, I'm bothered that R (or computers in general?) allows too many > ways to do the same thing that work SOME of the time. Without a very > deep understanding of the terminology, users are bewildered. > > Go read ?plotmath. Do we see "as.name"? NO. Why does the idiom > expression(paste()) work as well? (Don't answer, that's a rhetorical > question). > > There are too many ways to do the same thing. Or, well, too many of us > know one way that works sometime and don't find out it doesn't always > work until, as Bill says, it is buried in the bottom of some big > function that behaves erratically. > > Gabor notes this works (sometimes): > > plot(0, xlab = parse(text = xNm))
Actually, I was pointing out that that expression was as good as a longer expression that was posted and it always works (not just sometimes) if one interprets the problem as supplying the character representation of a plotmath expression in xNm -- this seems the logical generalization given that the example was the character representation of a plotmath expression. -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com ______________________________________________ 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.
