R help - Jun 2003 - combining mathematical notation and value substitution

Dear People,

I need to make a label which both contains math notation as well as
substitutes a value for an object. In the following label, len and theta
are one dim variables, and I am substituting their values appropriately.
This label looks fine except that I want the greek symbol for theta to
appear instead of the word `theta'. How can I do so most easily? I don't
understand the underlying mechanisms well enough to work it out for
myself. Thanks in advance.

Please cc me. I'm not subscribed to the list.

                                                           Faheem.

main=paste("Monotonic Multigamma run (n=",
deparse(substitute(len)),", ",
expression(theta),"=", deparse(substitute(theta)),").")

On Fri, 20 Jun 2003, Faheem Mitha wrote:
>
> Dear People,
>
> I need to make a label which both contains math notation as well as
> substitutes a value for an object. In the following label, len and theta
> are one dim variables, and I am substituting their values appropriately.
> This label looks fine except that I want the greek symbol for theta to
> appear instead of the word `theta'. How can I do so most easily?
[snip]
> main=paste("Monotonic Multigamma run (n=",
> deparse(substitute(len)),", ",
> expression(theta),"=", deparse(substitute(theta)),").")
Hmm. Tried this, didn't work either. Inspired by pg 32 of "R for
Beginners".

 main=paste("Monotonic Multigamma run",
           as.expression(substitute(n==length,list(length=len))),
           as.expression(substitute(theta==th,list(th=theta))))

                                            Faheem.

Faheem Mitha wrote:
> Dear People,
> 
> I need to make a label which both contains math notation as well as
> substitutes a value for an object. In the following label, len and theta
> are one dim variables, and I am substituting their values appropriately.
> This label looks fine except that I want the greek symbol for theta to
> appear instead of the word `theta'. How can I do so most easily? I
don't
> understand the underlying mechanisms well enough to work it out for
> myself. Thanks in advance.
> 
> Please cc me. I'm not subscribed to the list.
> 
>                                                            Faheem.
> 
> main=paste("Monotonic Multigamma run (n=",
> deparse(substitute(len)),", ",
> expression(theta),"=", deparse(substitute(theta)),").")
No, it won't work that way, because you have to specify an S expression 
in order to get mathematical annotation. An expression within paste() 
will be converted to a character string.

What you ca do is the other way round:


t1 <- theta     # you cannot use theta as variable and math. symbol
plot(1:10, main    substitute("Monotonic Multigamma run (" * n  == len
* ", " *
     theta == t1 * ").", list(len = len, t1 = t1)))


See also ?plotmath or that small article in R News:
Ligges (2002): R Help Desk: Automation of Mathematical Annotation in 
Plots. R News 2(3), 32-34.

Uwe Ligges

On Sun, 22 Jun 2003, Faheem Mitha wrote:
> If I'm doing this correctly, R does not seem to think it is a call.
>
> > is.call("Monotonic Multigamma run (" * n == len * ",
" * theta == t1
> * ").")
> Error in "Monotonic Multigamma run (" * n :
>         non-numeric argument to binary operator
R is trying to *evaluate*
  "Monotonic Multigamma run ("* n==len etc
which doesn't work.  Remember, is.call(), like any normal function, will
be passed the *value* of its arguments.

You could try
  is.call(quote("Monotonic Multigamma run("*n==len))
which is TRUE.
> It considers it a valid R expression though.
>
> > (mode(expression("Monotonic Multigamma run (" * n == len *
", " * theta
> == t1 * ").")))
> [1] "expression"
>
That's because expression() returns an expression.
>
> The clearest description I have seen of a call is in S Poetry, where it
> says
>
> "Mode call represents objects that are calls to a function. The first
> component of a call is the name (mode name) of the function being called.
> The rest of the call is the arguments given."
>
> This certainly is how calls are constructed using call(...), but I'm
not
> sure how it fits in with an expression like the one above. What is the
> function being called in that case, for example?
Well, we can find out. It must be either * or ==, but it isn't immediately
obvious which one ends up at the top level
> thing <- quote("Monotonic Multigamma Run ("*n==len* ",
" * theta
==t1*").")
> mode(thing)
[1] "call"
> length(thing)
[1] 3
> thing[[1]]
=> thing[[2]]
"Monotonic Multigamma Run (" * n == len * ", " *
theta
> thing[[3]]
t1 * ")."
> mode(thing[[2]])
[1] "call"
> mode(thing[[3]])
[1] "call"
> thing[[2]][[1]]
=> thing[[3]][[1]]
*

So it is a call to ==, with two arguments, each itself a call.  The first
arguemetn is also a call to == and the second is a call to *. And so on in
a tree structure.

> Maybe I'd understand this stuff better if I knew Lisp. I'm very
ignorant
> about programming language paradigms. I've looked at S Poetry, and S
> Programming. While they were helpful, I don't feel I've got a clear
> picture. Further recommended reading?
>
I don't know about further reading.  I think this is probably easier to
learn when you have a specific problem to solve.  I learned mostly by
porting the survival package.


	-thomas