How do I add legends when there are two y variables?-CodePudding

This is the code I used:

ggplot(Delays2006, aes(Month))   geom_point(aes(y = delay), color = "blue", size = 2) 
  geom_point(aes(y=delay2))   scale_x_discrete(limits=(month.name))
  labs(x= "Months", y = "Delays in minutes")   ggtitle(" Flight Data 2006")

This is the output:

May I ask how do I add legends to delay and delay2 in this graph. Thank you.

CodePudding user response：

If you want to have a legend you have to map on aesthetics, i.e. do geom_point(aes(y = delay, color = "delay")) geom_point(aes(y=delay2, color = "delay2")). Colors and labels could then be set via scale_color_manual.

Using mtcars as example data:

library(ggplot2)

ggplot(mtcars, aes(mpg))  
  geom_point(aes(y = hp, color = "hp"))  
  geom_point(aes(y = cyl, color = "cyl"))  
  scale_color_manual(values = c(hp = "blue", cyl = "green"), labels = c(hp = "Horse Power", cyl = "Cylinders"))