R help - Nov 2009 - How to concatenate expressions

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)

Hi,

You can try this, though I hope to learn of a better way to do it,

a = c(quote(alpha),quote(beta),quote(gamma))
b = lapply(1:3, function(x) as.character(x))
c = c(quote('-10'^th),
  quote('-20'^th),
  quote('-30'^th))

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

 text <-
   lapply(seq_along(a), function(ii) bquote(.(a[[ii]])*.(b[[ii]])*.(c[[ii]])))

 dev.new()

 plot(-5:5,-5:5,col=0)

 for (i in seq_along(a)) {
   text(x=i,
       y=i,
       labels=text[[i]])
 }
}

testplot(a,b,c)

HTH,

baptiste

2009/11/20 Sebastien Bihorel <Sebastien.Bihorel at
cognigencorp.com>:
> 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)
>
> ______________________________________________
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> PLEASE do read the posting guide
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>