Coloring a line plot based on a third factor in ggplot

Question

I am having a hard time with a coloring scheme in ggplot. If someone could help me out or send me to another question that would be fantastic.

I have data that look along the lines of

day=rep(1:10, 5)
year=rep(1992:1996, each=10)
state=rep(c("A","B"), each=25)
set.seed(4)
y=runif(50, 5.0, 7.5)
df=data.frame(year,day,state,y)
> head(df)
  year day state        y
1 1992   1     A 6.464501
2 1992   2     A 5.022364
3 1992   3     A 5.734349
4 1992   4     A 5.693437
5 1992   5     A 7.033936
6 1992   6     A 5.651069

I want to create a plot similar to the below. Using the code:

library(ggplot2)
p = ggplot(df, aes(day, y))
p = p + geom_line(aes(colour = factor(year)))
print(p)

I want the coloring to be based off of the state variable. I would like the years that are in state 'A' to be one color and the years in state 'B' to be another.

Thank you

Answer 1

If you want it separated by years but colored by state the key is to use the group= argument:

ggplot(data=df, aes(x=day, y=y, group=year, colour=state)) +
  geom_line() +
  geom_point()