[R] plotmath: how to create a vector of expressions?

[Marius Hofert]

Dear Peter,

perfect *as usual*, many thanks!

Cheers,

Marius

On 2011-02-26, at 17:55 , Peter Ehlers wrote:

> On 2011-02-25 15:57, Marius Hofert wrote:
>> Dear expeRts,
>> 
>> I would like to use LaTeX-like symbols in keys via plotmath. Below is a minimal
>> example. I get:
>> Error in fun(key = list(x = 0.5, y = 0.8, text = list(list(expression(paste("(",  :
>>   first component of text must be vector of labels
>> What's wrong? How can I create the required vector (of expressions)?
>> 
>> Cheers,
>> 
>> Marius
>> 
>> library(lattice)
>> val<- matrix(1, nrow = 10, ncol = 3)
>> nplot<- 10
>> 
>> labs<- sapply(1:3, function(i) substitute(expression(paste("(",i,"), ",l==len,"mm",sep="")), list(len=2*i)))
>> myplot<- xyplot(0~0,
>>                  panel=function(...){
>>                      for(i in 1:3){
>>                          panel.xyplot(1,val[,i],type="l")
>>                          panel.text(2,val[nplot,i],label=paste("(",i,")",sep=""))
>>                      }
>>                  },
>>                  key = list(x=0.5,y=0.8,text=list(labs),
>>                  align=TRUE,transparent=TRUE))
>> myplot
> 
> Try this:
> 
>  labs <- vector("expression", 3)
>  for(i in 1:3) labs[i] <-
>     substitute(expression(
>                  group("(", k, ")") * "," ~~ l == len ~ italic("mm")
>               ),
>               list(len = 2*i, k=i)
>     )[2]
> 
> The idea is to create an expression vector and then
> fill its components appropriately. We need the second
> component of the substitute call.
> (I put in the 'italic' just for fun.)
> 
> Maybe there's a better way, but I don't know it.
> 
> Peter Ehlers