1 Goal

The goal of this tutorial is to change the legent title in ggplot2.

2 Data import

# First we load the libraries
library(ggplot2)

# In this example we will use the open repository of plants classification Iris. 
data("iris")
str(iris)
## 'data.frame':    150 obs. of  5 variables:
##  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
##  $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
##  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
##  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
##  $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...
# Let's plot the petal length vs petal width
ggplot() + geom_point(data = iris, aes(x = Petal.Width, y = Petal.Length,color = Species))

3 Change the legend title

# We can change the plot title with scale_colour_manual
# However we need also to define the colors to be displayed
ggplot() + geom_point(data = iris, aes(x = Petal.Width, y = Petal.Length,color = Species)) +
  scale_colour_manual("Plant type", values = c("red", "darkgreen", "blue"))

4 Conclusion

In this tutorial we have learnt how to change the title of the legend in ggplot2.