ggplot2: geom_line() for single observations (x-factor, y-numeric)

Question

I have the following data and simple code

library(ggplot2)
dane <- data.frame(mylevels=c(1,2,5,9), myvalues=c(2, 5, 3, 4))
ggplot(dane, aes(x=factor(mylevels), y=myvalues)) + geom_line() + geom_point(size=3)

I'm not able to figure out how to force "ggplot2" to draw the line - I get an error. On pp. 55 (R Graphics Cookbook) Winston Chang describes the same error but my plot is simpler that's why his solution can't be adopted.

Answer 1

You should add group=1 inside aes() to connect points with line.

ggplot(dane, aes(x=factor(mylevels), y=myvalues,group=1)) + 
       geom_line() + geom_point(size=3)