[R] display double dot over character in plotmath?

[Berend Hasselman]

> 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.

Berend