R help - Nov 2004 - substitute/paste question for using Greek in plot titles

Hi all

I am having troubles making sense of why code (1)
below fails but code (2) below works.

Code (1):

 > phi.1 <- 1
 > plot(0 ~ 0,
+ main=substitute(paste("A vaue for ",phi," = ",phival), 
list(phival=phi.1)) )

Error in paste("The two deviances for ", phi, " = ", 2) :
         Object "phi" not found

But this works:

Code (2):
 > plot(0,0,
+ main=substitute(paste("A value for ",phi," = ",phival), 
list(phival=phi.1)) )
 >

It appears that if the plot command takes the formula style entry,
the substitue/paste fails.

Is this documented as a feature (I couldn't find it if that is the
case), or is it a bug?  If it is a feature, it is a subtle difference
between (1) and (2) that has potential to be quite frustrating!

Perhaps I should just upgrade to version 2.0.0, though I can't see
anything in the Release Notes that might cause this.

Thanks.

P.

 > version
          _
platform i686-pc-linux-gnu
arch     i686
os       linux-gnu
system   i686, linux-gnu
status
major    1
minor    9.1
year     2004
month    06
day      21
language R




-- 
Dr Peter Dunn          (USQ CRICOS No. 00244B)
   Web:    http://www.sci.usq.edu.au/staff/dunn
   Email:  dunn @ usq.edu.au
Opinions expressed are mine, not those of USQ.  Obviously...

Peter Dunn wrote:
> Hi all
> 
> I am having troubles making sense of why code (1)
> below fails but code (2) below works.
> 
> Code (1):
> 
>  > phi.1 <- 1
>  > plot(0 ~ 0,
> + main=substitute(paste("A vaue for ",phi," =
",phival),
> list(phival=phi.1)) )
> 
> Error in paste("The two deviances for ", phi, " = ", 2)
:
>         Object "phi" not found
> 
> But this works:
> 
> Code (2):
>  > plot(0,0,
> + main=substitute(paste("A value for ",phi," =
",phival),
> list(phival=phi.1)) )
>  >
> 
> It appears that if the plot command takes the formula style entry,
> the substitue/paste fails.
> 
> Is this documented as a feature (I couldn't find it if that is the
> case), or is it a bug?  If it is a feature, it is a subtle difference
> between (1) and (2) that has potential to be quite frustrating!
> 
> Perhaps I should just upgrade to version 2.0.0, though I can't see
> anything in the Release Notes that might cause this.
> 
> Thanks.
> 
> P.
> 
>  > version
>          _
> platform i686-pc-linux-gnu
> arch     i686
> os       linux-gnu
> system   i686, linux-gnu
> status
> major    1
> minor    9.1
> year     2004
> month    06
> day      21
> language R
> 
> 
Peter,

Because in the first couple of lines of plot.formula we see this:

dots <- m$...
dots <- lapply(dots, eval, data, parent.frame())

which for your case is equivalent to:

expr <- substitute(paste("A vaue for ",phi," = ",phival),
list(phival=phi.1))
eval(expr)

which returns an error saying "phi" cannot be found which is the
correct
behaviour of eval. I'll let others comment on whether or not this is a 
bug in plot.formula but you can always get around it by calling title:

plot(0 ~ 0)
title(main = expr)

which is exactly what your second example is doing in plot.default.

HTH,

--sundar