[R] Convert string for expression in plot

Richard Longland longland at physics.unc.edu
Tue Jan 29 21:33:15 CET 2008

Thanks for the help. This substitute command might be what I'm after,
but, the whole string is being read in from a file. So I can't
explicitly write the thing out as you did in your example, as with your
example in R-news.

My rules are:
Convert any ",g" or "g," to ",gamma" or "gamma,"
  (This comma search avoids converting the Mg to Mgamma!)
Make ANY number a superscript.

Currently, this is what I do:

# Read in the reaction name, not very elegant I know
ReacName <-

# convert and numbers and g
ReacName <- sub(",g",",gamma",ReacName)
ReacName <- sub("g,","gamma,",ReacName)
ReacName <- gsub("([1-9])","phantom()^\\1",ReacName)

This results in:

Just to clarify quickly, The text will always be different. The Mg could
be Al, S etc. The p could be different also. So the whole name has to be
automated into the plot title.

I imagine it's possible to split this string into pieces... but there
must be a better and easier way to do this.

Thanks again for the help,

On Tue, 2008-01-29 at 18:54 +0100, Uwe Ligges wrote:
> Richard Longland wrote:
> > Hi,
> > 
> > Although I understand how to use expression and paste to add
> > superscripts and symbols to my graphs, I have a problem with adding
> > superscripts to an existing string.
> > 
> > For example, I read in the following from a separate file:
> > 25Mg(p,g)
> > 
> > I want to convert that to superscripts etc. (in LaTex format):
> > $^{25}$Mg(p,$\gamma$)
> > 
> > This needs to then be put into a graph title.
> > 
> > Any ideas? I know that I can just write it in using expression and
> > paste, but the title is read in from a separate file.
> If you explain what the rules are to use superscript or greek letters 
> (why is the p not converted to pi but the g to gamma, etc?), we ca help,
> as an example if you read just the number from a file:
> #number <- scan(that_file)
> # say you read
> number <- 25
> plot(1:10, main=substitute(phantom()^number * Mg(p, gamma), 
> list(number=number)))
> See ?plotmath and for automating things like this my article in R News 
> might help:
> Ligges, U. (2002): R Help Desk: Automation of Mathematical Annotation in 
> Plots. R News 2 (3), 32-34.
> Best,
> Uwe Ligges
> > Cheers for the help,
> > Richard longland
> > 
> > ______________________________________________
> > R-help at 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.

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