How to change labels (legends) in ggplot?

Question

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 len         


        

Answer 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.