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.
