How to change labels (legends) in ggplot?

问题

My code is like below, I want to change the label of the ggplot, but R always remind me:

Error in unit(tic_pos.c, "mm") : 'x' and 'units' must have length > 0

What should I do?

ggplot(mat,aes(x=sales,col=type))+
  geom_density()+labels("red_sold","blue_sold","yellow_sold")

回答1:

Is mat$type a factor? If not, that will cause the error. Also, you can't use labels(...) this way.

Since you did not provide any data, here's an example using the built-in mtcars dataset.

ggplot(mtcars, aes(x=hp,color=factor(cyl)))+
  geom_density()+
  scale_color_manual(name="Cylinders",
                       labels=c("4 Cylinder","6 Cylinder","8- Cylinder"),
                       values=c("red","green","blue"))

In this example,

ggplot(mtcars, aes(x=hp,color=cyl))+...

would cause the same error that you are getting, because mtcars$cyl is not a factor.

来源：https://stackoverflow.com/questions/23161897/how-to-change-labels-legends-in-ggplot