R help - Jan 2003 - Varying texts in expression(paste())

Hi,

I am using R a lot to make plots relating to radioactivity, I am often using
expression() to label the plots with nuclide names written with
superscripts, e.g. 
	expression(paste("Releases of ", { }^{99},Tc,"
(TBq/year)"))->ywtext
But, is there any simple way to change the number and name of the nuclide
through a variable? I tried 
	nuccode=expression({ }^{99},Tc)
expression(paste("Releases of ", as.expression(nuccode) ,"
(TBq/year)"))->ywtext

But, obiously, since as.expression does not return a chr, it was used
literally in the text on the figure, i.e. "Releases of
as.expression(nuccode) (TBq/year)" which definiately was not what I
wanted... 

should I use some other wrapper function on the expression, or are there
some other ways of making superscripts in figure texts?

regards

Morten

-- 
Morten Sickel
Norwegian Radiation Protection Authority
http://www.nrpa.no

Hi,

I had a similar problem last year and Thomas Lumley helped me a lot on this. I
needed to replace some variables by their values in a quite complicated text
expression. Here is what Thomas suggested:

<quote Thomas Lumley on>
In your example you wanted b and c to be elements of a vector.  They
actually have to be elements of a list
> c(quote(beta),quote(gamma^3))
[[1]]
beta

[[2]]
gamma^3

So
 expr1<-quote(alpha)
 expr2<-c( quote(beta), quote(gamma^3))
 plot(1:10,main=substitute("Estimated "*a*" for "*b*"
vs."*c,
        list(a=expr1,b=expr2[[1]],c=expr2[[2]])))

Finally, you could even make the expressions from text strings if you want
to

str1<-"alpha"
str2<-c("beta","gamma^3")

expr1<-parse(text=str1)[[1]]
expr2<-parse(text=str2)
 plot(1:10,main=substitute("Estimated "*a*" for "*b*"
vs."*c,
        list(a=expr1,b=expr2[[1]],c=expr2[[2]])))

<quote Thomas Lumley off>
For full details see (and this is worthwhile!) the thread "[R] Constructing
titles from list of expressions" from August 7, 2002.

Thanks again to Thomas,

Winfried

---------------------------------------------------------------------
E-Mail: Winfried Theis <theis at statistik.uni-dortmund.de>
Date: 31-Jan-03

Dipl.-Math. Winfried Theis
SFB 475, Fachbereich Statistik, Universit"at Dortmund, 44221 Dortmund
Tel.: +49-231-755-5903 FAX: +49-231-755-4387
----------------------------------------------------------------------

Gunter Bart wrote:
> You need substitute(). Look at the examples in plotmath().
> x<-3;y<-'foo'
> plot(c(0,1),c(0,1),type='n')
> text(.5,.5,substitute(paste('Releases of ',x^99,' ',y,'
> TBq/year'),list(x=x,y=y)))
> Hope this helps ...
Thanks a lot, it helped indeed!

Morten