[R] plotmath question

[Thomas Lumley]

On Fri, 18 Mar 2005, Berton Gunter wrote:
>
> 2) The plotmath Help state that expressions can be used for axis labels, so
> I would have expected the above to work without the eval()call  -- but it
> does not. Would someone kindly explain to me why not -- i.e., what I have
> misunderstood. That is, to be clear, why does the following not work:

Because substitute() doesn't evaluate its argument: the result is not an 
expression but a call to the expression() function.

An example where it is clearer what is going on

substitute(log(x),list(x=1))

doesn't return a number, even though log() returns a number. It returns a 
call to log() that still has to be evaluated

 	-thomas

> for(i in seq(-3,to=3))
> 	axis(1,at=i, lab=switch(sign(i)+2,
> 			substitute(expression(mu-j*sigma),list(j=i)),
> 			expression(mu),
> 			substitute(expression(mu+j*sigma),list(j=i))))
>