[R] How to concatenate expressions

[Sebastien Bihorel]

Dear R-users,

I am developing a plotting function, which receives expressions and 
character/numerical vectors as part of the many input arguments and 
which tries to concatenate them before displaying the result to the 
plot. I currently cannot find a way to make this concatenation works. I 
have read several posts in the list that solved this problem by pasting 
the different elements together before creating the expressions (like in 
http://tolstoy.newcastle.edu.au/R/help/02a/4790.html). I cannot 
implement this solution because my expressions and numerical/character 
vectors are passed to the function and not create inside the function. I 
would greatly appreciate any help with the following example code.

Thank you


testplot <- function(a,b,c) {

  text <- as.expression(paste(a,b,c,sep=' '))

  dev.new()
 
  plot(-5:5,-5:5,col=0)

  for (i in 1:3) { 
    text(x=i,
         y=i,
         labels=text[i])
  }
}

a <- as.expression(c(bquote(alpha),bquote(beta),bquote(gamma)))

b <- as.expression(1:3)

c <- as.expression(c(bquote('-10'^th),
                     bquote('-20'^th),
                     bquote('-30'^th)))

testplot(a,b,c)