Add legend to geom_line() graph in r

Question

I\'ve been trying to add legend to my ggplot, but failed miserably. I tried the function scale_colour_manual(), but the legend doesn\'t show up.

Answer 1

To provide a more compact answer which only uses a single geom call:

ggplot2 really likes long data (key-value pairs) better than wide (many columns). This requires you to transform your data prior to plotting it using a package like tidyr or reshape2. This way you can have a variable denoting color, inside your aes call, which will produce the legend.

For your data:

library(tidyr)
library(ggplot2)

plot_data <- gather(data, variable, value, -x)

ggplot(plot_data, aes(x = x, y = value, color = variable)) +
  geom_line() +
  scale_color_manual(values = c("firebrick", "dodgerblue")) 

You can then customize the legend via scale_color series of helpers.