R help - Dec 2006 - How to use strings from a data.frame as the argument of an expression() for plot

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.

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.
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Thanks for your response; one more thing: Is it
possible to use a data.frame 
for the same effect, as these values are associated
with some others (I could 
of course use them separately, but merging them in a
data.frame should be 
possible in R)?
> 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.
>

Just store them as strings in the data frame and then perform a conversion
to expressions prior to the loop:


DF <- data.frame(s = c("O[3]", "NO", "NO[2]"),
stringsAsFactors = FALSE)
e <- parse(text = DF$s)
... continue with prior solution ...

On 12/20/06, MrJ Man <auxsvr at yahoo.com> wrote:
> Thanks for your response; one more thing: Is it
> possible to use a data.frame
> for the same effect, as these values are associated
> with some others (I could
> of course use them separately, but merging them in a
> data.frame should be
> possible in R)?
>
> > 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.
> >
>
>
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