[R] display double dot over character in plotmath?

[Ranjan Maitra]

On Sat, 13 May 2017 20:25:41 +0200 Berend Hasselman <bhh at xs4all.nl> wrote:

> 
> > On 13 May 2017, at 20:10, David Winsemius <dwinsemius at comcast.net> wrote:
> > 
> >> 
> >> On May 13, 2017, at 5:47 AM, Ranjan Maitra <maitra at email.com> wrote:
> >> 
> >> 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.
> > 
> > On a Mac it is cmd-u followed by the vowel of your choice. Perhaps you should do a google search on the topic of getting umlauted characters for the distro of your choice?
> > 
> 
> Option u followed by vowel! If you haven't changed Modifier Keys.

Thanks! I could not figure this out yet, butI was thinking: can I not use the ascii key (I guess it would be 0228) then? But how would I do this? Btw, I really would like to use omega  in an example but I figured that the usual way of writing Greek characters would work there.

I tried the following:

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~"\0228"(omega)))))

but I do not get what I want. Looking around, it is not clear to me that I can get this to work. The ASCII codes that I saw were all specific to a letter with umlaut. I want \omega with the double dots (umlaut).

Thanks again!
Best wishes,
Ranjan