Hi,
I'm trying to understand whether the use of substitute() is
appropriate/documented for plotmath annotation. The following two
calls give the same results:
> plot(1:10, main = expression(alpha == 1))
> do.call(plot, list(1:10, main = expression(alpha == 1)))
But not these two:
> plot(1:10, main = substitute(alpha == a, list(a = 2)))
> do.call(plot, list(1:10, main = substitute(alpha == a, list(a = 2))))
Error in as.graphicsAnnot(main) : object "alpha" not found
(as a consequence, xyplot(..., main = substitute(alpha)) doesn't
currently work.)
On the other hand, this works:
> foo <- function(x) plot(1, main = x)
> foo(substitute(alpha))
I'm not sure how to interpret ?plotmath; it says
If the 'text' argument to one of the text-drawing functions
('text', 'mtext', 'axis', 'legend') in R is an expression, the
argument is interpreted as a mathematical expression...
and uses substitute() in its examples, but
> is.expression(substitute(alpha == a, list(a = 1)))
[1] FALSE
-Deepayan
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