Throwing an error when duplicated timestamps encountered?

[Jie Bao]

Hi all,

I recently came across an example timeseries dataset when a block of timestamps were duplicated, and when I plotted it with ggplot, it generated a strangely looking curve. It seems that it is allowed to use geom_line to connect dots even if there're multiple y values for a single x (this is of course totally fine with facets, but it's meaningless in a single plot). Would it make sense to throw some error in this case? 

Best,

Jie