[R] expression() and axis labels

[David Winsemius]

On Jul 16, 2011, at 12:09 PM, Thomthom wrote:

> Hi everyone!
>
> I tried to look up in the previous topics whether there was something
> similar to my question but I think there's nothing corresponding...
>
> Anyway! Here is my problem:
>
> I have a plot (qplot()) in which I want to insert axis labels with the
> following text:
>
> kg NH4+ N-equiv. * ha-1 yr-1 (well... 4 smaller and down and + as a  
> power
> (the same for the -1) but I am sure you understood what I meant).
>
> So, in my code, I typed :
>
> qplot(...., xlab="Amount of N-fertilizer" expression(kg NH[4]^+ N- 
> equiv. *
> ha^-1 yr^-1))

I have never see a successful concatenation of regular text in quotes  
with expression(...), so my efforts were focussed on making a  
sytactically correct expression:

plot(1~1, xlab=expression(Amount~of~N-fertilizer~kg~NH[4]^"+"*"*"*N- 
equiv.~
ha^-1*yr^-1) )


You need to forget about spaces as separators since they are ignored,   
and use either "~" or "*" as connectives and that also means that if  
you want "*" to appear, it needs to be quoted.

plot(1~1, xlab=expression(Amount~of~N-fertilizer~kg~ NH[4]^ "+" *   
"*"  *  N-equiv.~
ha^-1 * yr^-1) )  # spaces added bak to show grouping, but they are  
still ignored.

I'm guessing you want the last part in parens:

plot(1~1, xlab=expression(Amount~of~N-fertilizer~kg~ NH[4]^ "+" *
                        group("(", list( N-equiv.~ ha^-1 * yr^-1),  
")" ))

-- 
David

>
> but I don't get what I expect... everything after the first "^" is
> considered as a power, whereas I would like to have only the + and  
> the -1 as
> a power.
>
> Is there a way to obtain what I want? somehow to split up the  
> expression so
> I don't get everything put at the power of NH4.
>
> I already thank you guys for your help!!!
>
> Thomthom
>
> --
> View this message in context: http://r.789695.n4.nabble.com/expression-and-axis-labels-tp3672050p3672050.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org 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.

David Winsemius, MD
West Hartford, CT