plotmath: paste string and expression [from a vector of expressions]

Dear Dennis, Dear Uwe, Dear David,

many thanks for helping. Dennis and David, your solutions seemed  
perfectly fine, but when I applied it to my original problem, it did  
not show a title. Below is a (longer) minimal example (the first  
part is from the help page of bbmle). Is this a bug in bbmle? Hmmm...

library(bbmle)

x <- 0:10
y <- c(26, 17, 13, 12, 20, 5, 9, 8, 5, 4, 8)
d <- data.frame(x,y)

## in general it is best practice to use the `data' argument,
##  but variables can also be drawn from the global environment
LL <- function(ymax=15, xhalf=6)
   -sum(stats::dpois(y, lambda=ymax/(1+x/xhalf), log=TRUE))

## uses default parameters of LL
(fit <- mle2(LL))
ml <- mle2(LL, fixed=list(xhalf=6))
mlp <- profile(ml)

vars <- c(quote(theta), quote(beta))
plot(mlp, main=bquote(bold("Foo"~.(vars[[2]]))))

I do not have experience with that package but my guess is that the  
plot.mle2 (or whatever its name might be... )  function does something  
different. class(mlp) returns "profile.mle2". Looking at the  
documentation you see that it is using S4 methods and using Methods()  
one sees that there is a 'plot' method for 'profile.mle2' objects.  
That's about as far as I go.

<whine-mode on>
  Navigating S4 methods is an arcane art into which I have not  
initiated myself. Unlike S3 methods where you just type the function  
name and it's easy to figure out what the names will be, there are  
several levels of specification and the help pages for "Methods' ....  
are not, ... "helpful" to one who approaches it without more  
experience than I have. The help page regarding acceptable expressions  
to pass to "main" arguments is not particularly helpful, either. I  
would advise asking the package author or maintainer.

Before anyone berates me for insufficient effort at self-learning, I  
swear that my copy of Chambers (2008) arrived this week. I do think it  
would be "helpful" to have a worked example near the top of examples  
on help(Methods) that shows HOW_TO get at the functional machinery for  
a plot method when one knows the class of an object.

After some further experimentation I have a theory that the 'main'  
argument will not accept a language object but that one can coerce to  
an expression object and succeed. (Didn't I go through this once  
before? Maybe this was what Hadley was trying to teach me about a  
month ago.)
<whine-mode off>

# -----Answer

plot(mlp, main=as.expression(bquote(bold(Foo~.(vars[[2]])  )) ) )

# --- back your regularly scheduled programming -------

DAvid.


>
> Cheers,
>
> Marius
>
> On 2011-06-02, at 22:23 , Dennis Murphy wrote:
>
>> Hi:
>>
>> This seems to work:
>>
>> vars2 <- c(quote(alpha), quote(beta))   # returns a list of mode call
>> plot(0, 0, main = bquote(bold('Foo '~.(vars2[[2]]))))
>>
>> Expressions are only evaluated once, which means that inner
>> expressions are not evaluated. You need a call object rather than an
>> expression inside of bquote().
>>
>> HTH,
>> Dennis
>>
>> On Thu, Jun 2, 2011 at 11:43 AM, Marius Hofert <m_hofert at web.de>  
>> wrote:
>>> Dear all,
>>>
>>> I have a vector of expressions and would like to "paste" some  
>>> string to it before using it in a plot:
>>>
>>> vars <- vector("expression", 2)
>>> vars[1] <- expression(alpha)
>>> vars[2] <- expression(beta)
>>> plot(0, 0, main=substitute(bold("Foo" ~~ VAR), list(VAR=vars[2]) ))
>>>
>>> Although I tried hard, I just can't figure out how to solve this.  
>>> The title should be "Foo <theta>", where <theta> is the greek  
>>> letter. I tried some constructions with bquote but that wasn't  
>>> successful... I also looked in the mailing list but couldn't find  
>>> anything helpful [I am sure I overlooked something].
>>>
>>> Cheers,
>>>
>>> Marius
>>>
>>> ______________________________________________
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>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>

David Winsemius, MD
West Hartford, CT