How to deal with “data of class uneval” error from ggplot2?

Question

While trying to overlay a new line to a existing ggplot I am getting the following error:

Error: ggplot2 doesn\'t know how to deal with data of class uneval         


        

Answer 1

when you add a new data set to a geom you need to use the data= argument. Or put the arguments in the proper order mapping=..., data=.... Take a look at the arguments for ?geom_line.

Thus:

p + geom_line(data=df.last, aes(HrEnd, MWh, group=factor(Date)), color="red") 

Or:

p + geom_line(aes(HrEnd, MWh, group=factor(Date)), df.last, color="red")