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
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