[R] How to use strings from a data.frame as the argument of an expression() for plot

[Gabor Grothendieck]

Try this:


e <- expression(O[3], NO, NO[2])
opar <- par(mfrow = c(2,2))
for(i in 1:3) plot(1, 1, type = "b", main = bquote(.(e[[i]]) ~ Year ~ 2005))
par(opar)

Also please read the last line to every post to r-help and particularly note
the part about reproducible examples.   x and y.were undefined.

On 12/20/06, MrJ Man <auxsvr at yahoo.com> wrote:
> Greetings,
>
> I would like to use a data.frame with strings to feed
> the expression() in the title of a plot. The way I did
> this is:
>
> molecules
> <-data.frame(name=c("o3","no","no2"),expression=c("quote(O[3])","quote(NO)","quote(NO[2])"))
>
> for (mol in c(5,7,9)) {
>  plot(x, y, type="b",
> main=eval(substitute(expression(paste(mol," Year
> 2005")),
>
> list(mol=eval(parse("",text=toString(molecules$expression[(mol-3)/2])))))))
> }
>
> However, this looks cumbersome and I'm sure there is a
> way to do this in R that is much more simple. The
> complexity of the expression above is mainly due to
> the fact that the only way I could find to convert a
> string read from a data.frame into a symbol was to
> enclose it in "quote(symbol)" and call toString on the
> result, since selecting string data from a data.frame
> returns an object that is not a string (why is this
> so? A data.frame with doubles returns doubles).
>
> What do you think?
>
> Thanks in advance.
>
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