add mean line to ggplot

Question

I\'d like to build on this example of conditioning line color on slope to add a line for the mean (line from mean t=1 to mean t=2).

library(dplyr)
set.seed(2         


        

Answer 1

I didn't get the error you describe (with ggplot2 v 2.2.0), but in order to get the desired result I did have to override the grouping you specified in the main plot:

stat_summary(fun.y=mean,geom="line",lwd=2,aes(group=1))