[R] ggtern and bquote...

[Martin Maechler]

>>>>> peter dalgaard <pdalgd at gmail.com>
>>>>>     on Mon, 4 Dec 2017 14:55:19 +0100 writes:

    >> On 4 Dec 2017, at 11:58 , Levent TERLEMEZ via R-help
    >> <r-help at r-project.org> wrote:
    >> 
    >> Dear Users,
    >> 
    >> What is the proper way to write symbol, superscript,
    >> subscript in ggtern/ggplot? I tried every given example,
    >> every possible features of ggplot but couldn’t achived. I
    >> just want to write P_a, sigma^2, etc, would you please
    >> advise me about this problem.

    > Did you try expression(P_a)? I don't do much gg-stuff, but
    > I seem to recall that quote() doesn't quite cut it the way
    > it does in base graphics.

    > -pd

Yes, I vaguely remember that indeed also for the lattice package
(which is based on 'grid' the same as 'ggplot2' is ..) sometimes
expressions instead of calls are needed, i.e., expression(*)
instead of just quote(*).

However, I think Levent really meant what you'd get by
 expression(P[a]) ?

@Levent: The clue is the need for valid R syntax, and indeed, as
   in LaTeX  x_i often is the i-th element of x,  the R syntax for
   indexing/subsetting is used here, i.e.
    x[i]  for LaTeX  x_i


Last but not least, if Levent really needs bquote() [i.e. substitute()]
then, a final
      as.expression(.)
may be needed :

identical(as.expression(quote(a == 1)),
	     expression(      a == 1))  # --> TRUE

--
Martin Maechler, ETH Zurich