[R] surprising behaviour of "bgroup": sets all in greek letters

[Uwe Ligges]

Ulf Martin wrote:
> Dear R user community
> 
> I wanted to use "bgroup" for plotting a math formula with
> a big "{" on the left, and nothing on the right.
> i used
> 
>   text( 10, 10, pos=4, cex=1.8, expression(F(x) == bgroup("{", x, "")), ...)
> 
> on a 40 x 20 plot.
> surprisingly,
> bgroup sets "Phi(xi) = { xi" 
> i.e. replaces alphabetic characters with greek letters in the entire formula.
> 
> I tried out other ending delimiters instead of "":
> With " ", ":", ";", ",", R complains about an "invalid group delimiter",
> With "." R produces greek letters again.
> 
> Is this a bug, or am I missing something?
> How could I possibly accomplish my original task?
> The idea is to have something like
> 
>           0 if x<0
>  F(x) = {
>           y otherwise
> 
> in the end.
> 
> Thanks in advance!
> (and for the great tool anyway!)
> 
> (I am not currently subscribed to the r-help list,
> so I would be gratful if anybody could answer me directly too, thanks!)
> 
> Bye

Looks like a bug. I'll investigate further within the next couple of 
days (except anyone else comes up with the right idea before).

Uwe Ligges