R help - Jan 1999 - r-help[Q]: use of `expression' in annotation

Dear r-helpers,

I have some multiplot figures that I would like to annotate.  To each plot
frame I would like to add the associated correlation coefficients.  To do
so, I believe I need to understand the usage of `expression' better.  

The following is a good start.

  petstring <- expression(paste(r[rho*p],"=" ))
  mtext(petstring, line=0.3, adj=0.1, cex=0.8) 

My question is, how can I interpolate a variable into this expression?  

I would like petstring to contain r[rho*p] = peti, where peti is the corr.
coefficient that would vary across panes in the figure.  I have tried
various combinations of paste and expression and have not hit on the right
combination (instead I usually get peti as a literal rather than a
variable).

Thanks, Alex Buerkle

~^^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^
C. Alex Buerkle                 Ph:  812-855-9018
Jordan Hall 142                 Fax: 812-855-6705
Department of Biology           
Indiana University
Bloomington, IN 47405    cbuerkle at bio.indiana.edu

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Alex Buerkle <cbuerkle at bio.indiana.edu> writes:
> I would like petstring to contain r[rho*p] = peti, where peti is the corr.
> coefficient that would vary across panes in the figure.  I have tried
> various combinations of paste and expression and have not hit on the right
> combination (instead I usually get peti as a literal rather than a
> variable).
Consider the following:

plot(0:11,type='n')
for (x in 1:10) 
   text(x,x,as.expression(substitute(r[rho*p] == peti,list(peti=x/10))))

[which probably also indicates that the as.char.or.expr() function
used inside text() could use modification! The as.expression bit
should be avoidable on objects of mode call.]
-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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