How to Assign Colors by Factor in ggplot2 (With Examples)

Often you may want to assign colors to points in a ggplot2 plot based on some categorical variable.

Fortunately this is easy to do using the following syntax:

ggplot(df, aes(x=x_variable, y=y_variable, color=color_variable)) +
  geom_point()

This tutorial provides several examples of how to use this syntax in practice using the built-in R dataset titled iris:

#view first six rows of iris dataset
head(iris)

  Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1          5.1         3.5          1.4         0.2  setosa
2          4.9         3.0          1.4         0.2  setosa
3          4.7         3.2          1.3         0.2  setosa
4          4.6         3.1          1.5         0.2  setosa
5          5.0         3.6          1.4         0.2  setosa
6          5.4         3.9          1.7         0.4  setosa

Example 1: Use Default Colors

The following code shows how to assign default colors to the points in a ggplot2 plot based on the factor variable Species:

library(ggplot2)

ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, color=Species)) +
  geom_point()

color by factor in ggplot2

Since we didn’t specify a color scale or a list of custom colors, ggplot2 simply assigned a list of default red, green, and blue colors to the points.

Example 2: Use Custom Colors

The following code shows how to assign custom colors to the points in a ggplot2 plot by using scale_color_manual():

library(ggplot2)

ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, color=Species)) +
  geom_point() +
  scale_color_manual(values = c("setosa" = "purple",
                                "versicolor="orange",
                                "virginica"="steelblue"))

ggplot2 with custom colors for categorical variable

Note that we could have used hex color codes as well to specify the colors.

Example 3: Use a Custom Color Scale

The following code shows how to assign custom colors to the points in a ggplot2 plot by using a custom color scale from the RColorBrewer package:

library(ggplot2)
library(RColorBrewer)

#define custom color scale
myColors <- brewer.pal(3, "Spectral")
names(myColors) <- levels(iris$Species)
custom_colors <- scale_colour_manual(name = "Species Names", values = myColors)

ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, color=Species)) +
  geom_point() +
  custom_colors

RColorBrewer example in R