R help - Sep 2012 - Sub- or superscript in factorial variable - possible?

Hello R-users,

I would like to use subscript in chemical formulas for the different 
treatments in a boxplot.
Fot title, xlab and ylab sub- and superscript is no problem, but for the 
different treatments of the following example I cannot get subscript.

Example:
weight <-  c(6,5,7,2,7,3,9,4,2,7,8,9,2,3,4,5)
treatments <- as.factor(rep(c('Control',
'P2O5','K2SO4','CaSO4'),4))
data <- data.frame(treatments,weight)
boxplot(data$weight~data$treatments)

If I apply expression(P[2]...) I get  "unimplemented type
'expression'
in 'HashTableSetup' ".
If there is a solution for this in base graphics or ggplot please let me 
know.

Thanks in advance,
Michael

On Sep 15, 2012, at 7:15 PM, mcg wrote:
> Hello R-users,
> 
> I would like to use subscript in chemical formulas for the different
treatments in a boxplot.
> Fot title, xlab and ylab sub- and superscript is no problem, but for the
different treatments of the following example I cannot get subscript.
> 
> Example:
> weight <-  c(6,5,7,2,7,3,9,4,2,7,8,9,2,3,4,5)
> treatments <- as.factor(rep(c('Control',
'P2O5','K2SO4','CaSO4'),4))
> data <- data.frame(treatments,weight)
> boxplot(data$weight~data$treatments)
> 
> If I apply expression(P[2]...) I get  "unimplemented type
'expression' in 'HashTableSetup' ".
> If there is a solution for this in base graphics or ggplot please let me
know.
> 
?plotmath
 boxplot(data$weight~data$treatments, xaxt="n")
 axis(1, 1:4, labels=expression(Control, P[2]*O[5], K[2]*SO[4], CaSO[4]) )

I will admit that the need for the "*"'s was not apparent to me
until I used the initial example as a starting point and made incremental
changes until I gotsuccess. So I am not suggesting that RTM should have been
enough.

-- 
David Winsemius, MD
Alameda, CA, USA