How does one get a legend to display when plotting lines in ggplot? I've been trying all evening but have been unsuccessful.
p <- ggplot(output, aes(lambda), legend=TRUE) +
geom_line(aes(y=train.err), colour="red", label="r") +
geom_line(aes(y=test.err), colour="blue", label="b") +
geom_line(aes(y=data.err), colour="green", label="g")
print(p)
Where output is a dataframe with the following structure:
'data.frame': 2101 obs. of 4 variables:
$ lambda : num 3.06e-07 3.09e-07 3.12e-07 3.15e-07 3.18e-07 ...
$ train.err: num 0.415 0.415 0.415 0.415 0.415 ...
$ test.err : num 0.373 0.373 0.373 0.373 0.373 ...
$ data.err : num 0.398 0.398 0.398 0.398 0.398 ...
put colour inside the aes like this:
d<-data.frame(x=1:5, y1=1:5, y2=2:6)
ggplot(d, aes(x)) +
geom_line(aes(y=y1, colour="1")) +
geom_line(aes(y=y2, colour="2")) +
scale_colour_manual(values=c("red", "blue"))
but I recommend this way:
d2 <- melt(d, id="x")
ggplot(d2, aes(x, value, colour=variable)) +
geom_line() +
scale_colour_manual(values=c("red", "blue"))