[R] display double dot over character in plotmath?

[Ranjan Maitra]

On Fri, 12 May 2017 23:39:14 -0700 Daniel Nordlund <djnordlund at gmail.com> wrote:

> On 5/12/17 4:55 PM, Ranjan Maitra wrote:
> > Hi,
> > 
> > Is it possible to display double dot (umlaut) over a character such as would be possible using \ddot x in LaTeX? I can do this using tikzDevice but I wanted something simpler to point to.
> > 
> > Here is an example of what I would like to do, but it is not quite there:
> > 
> > require(ggplot2)
> > data<-as.data.frame(c("a","b","c","a","b","c"))
> > colnames(data)<-"Y"
> > data$X<-c(1:6)
> > data$Z<-c(1,2,3,1,2,3)
> > 
> > ggplot(data, aes(x=X)) + geom_line(aes(y = Z), size=0.43) + xlab(expression(atop(top,bold(Age~"à"))))
> > 
> > I would like to put in a double dot over the "a" in the x-axis instead of "`".
> > 
> > Many thanks for any suggestions and best wishes,
> > Ranjan
> > 
> 
> You haven't told what OS you are using, but with Windows OS, you can get 
> the 'ä' by making sure the NUMLOCK key is on, hold down the alt key and 
> press 0228 on the numeric keypad.
> 
> 

I am sorry, I use a linux operating system. I use Fedora 25 but the student I wanted to show this uses Ubuntu, though I don't know if the distribution matters.

Thanks again for your help, and best wishes,
Ranjan