geom_sina() is does not provide output images and stops on one of my machines (Ubuntu 16.04.5 LTS; sessionInfo attached below). All geom_sina() calls generate the same warning message:
Computation failed in stat_sina():
Please use to_lower_ascii(), which works fine in all locales.
All generated images have the base graphics, but none of the individual points that would be generated through geom_sina(). I've taken a look at the traceback() and in other issues, but I'm not sure what that warning message means (and why exactly the computation stops, and the images are effectively empty).
I see the following problem with real data and illustrative data. An illustrative example is below (generated in a similar way from a prior issue: #48).
df <- data.frame(g=c("A","B"),v=rnorm(100))
ggplot(df, aes(x=g,y=v)) + geom_point() ##works
ggplot(df, aes(x=g,y=v)) + geom_violin() ##works
ggplot(df, aes(x=g,y=v)) + geom_sina() ##does not work
R version 3.4.3 (2017-11-30)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 16.04.5 LTS