Scatter plot by group in ggplot2

Sample data

The data below contains two numerical variables and a categorical variable representing groups. This data frame be used in the following examples.

set.seed(1)

# Data simulation
x <- runif(500)
y <- 5 * x ^ 2 + rnorm(length(x), sd = 2)
group <- ifelse(x < 0.4, "A",
                ifelse(x > 0.8, "C", "B"))
x <- x + runif(length(x), -0.2, 0.2)

# Data frame
df <- data.frame(x = x, y = y, group = group)

Scatter plot by group with geom_point

Creating a scatter plot by group in ggplot2 is straightforward, as you only need to pass the categorical variable to the color argument of aes.

# install.packages("ggplot2")
library(ggplot2)

# Scatter plot by group
ggplot(df, aes(x = x, y = y, color = group)) +
  geom_point()

Scatter plot by group in ggplot2

Changing the colors

The default color palette can be customized in several ways. You can use scale_color_manual and pass a vector of colors to the values argument or choose a predefined discrete palette, such as scale_color_viridis_d.

# install.packages("ggplot2")
library(ggplot2)

# Vector of colors
cols <- c("#1170AA", "#55AD89", "#EF6F6A")

ggplot(df, aes(x = x, y = y, color = group)) +
  geom_point() +
  scale_color_manual(values = cols)

Scatter plot by group in ggplot2 color scale

Changing the shape and the size

The default shape of the observations are filled circles, but you can choose any symbol with shape. The size of the symbols can also be customized, making use of size.

# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = x, y = y, color = group)) +
  geom_point(shape = 17, size = 2)

Scatter plot symbol in ggplot2

Shape by group

If you want you can add a different shape by group, pass the grouping variable to the shape argument of the aes function. Note that you can specify this argument without setting color.

# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = x, y = y, color = group,
               shape = group)) +
  geom_point(size = 2)

Scatter plot with shape by group in ggplot2

Legend customization

ggplot2 scatter plot with custom legend

Legend title

When you create a scatter plot by group in ggplot2 an automatic legend is created based con the categorical variable. The default title of the legend is the name of the variable, but you can override this with the following code.

# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = x, y = y, color = group)) +
  geom_point(size = 2) +
  guides(colour = guide_legend(title = "Title"))

Scatter plot by group in ggplot2 with custom key labels

Custom key labels

The labels can also be customized. You can make use of the labels argument of the scale_color_discrete function to change them.

# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = x, y = y, color = group)) +
  geom_point(size = 2) +
  scale_color_discrete(labels = c("G1", "G2", "G3"))

Remove the legend in ggplot2 scatter plot

Remove the legend

In case you want to get rid of the legend set legend.position = "none" inside the theme function.

# install.packages("ggplot2")
library(ggplot2)

ggplot(df, aes(x = x, y = y, color = group)) +
  geom_point(size = 2) +
  theme(legend.position = "none")
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See also