Plotting a time series where color depends on a category with ggplot

Question

Consider this minimum working example:

library(ggplot2) 
x <- c(1,2,3,4,5,6)
y <- c(3,2,5,1,3,1)
data <- data.frame(x,y)
pClass <- c(0,1,1,2,2,0)

plottedGraph <- ggplot(data, aes(x = x, y = y, colour = factor(pClass))) + geom_line()
print(plottedGraph)

I have a time series y = f(x) where x is a timestep. Each timestep should have a color which depends on the category of the timestep, recorded in pClass.

This is the result it gives:

It doesn't make any kind of sense to me why ggplot would connect points with the same color together and not points that follow each other (which is what geom_line should do according to the documentation).

How do I make it plot the following:

Answer 1

You should use group = 1 inside the aes() to tell ggplot that the different colours in fact belong to the same line (ie. group).

ggplot(data, aes(x = x, y = y, colour = factor(pClass), group = 1)) + 
  geom_line()