Change Alpha of Points in Plot – Base R & ggplot2 (2 Examples)

In this article you’ll learn how to decrease the alpha of points in an xy-plot using Base R and the ggplot2 package in the R programming language.

Preparing the Examples

data(iris)                                                     # Loading iris data set
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: Decrease Alpha in Base R Scatterplot

plot(iris$Petal.Length,                                        # Graph without transparency
     iris$Petal.Width,
     cex = 6,
     pch = 16,
     col = iris$Species)

r graph figure 1 change alpha points base r ggplot2

install.packages("scales")                                     # Install & load scales
library("scales")
plot(iris$Petal.Length,                                        # Transparent graph
     iris$Petal.Width,
     cex = 6,
     pch = 16,
     col = alpha(as.numeric(iris$Species), 0.5))

r graph figure 2 change alpha points base r ggplot2

Example 2: Decrease Alpha in ggplot2 Scatterplot

install.packages("ggplot2")                                    # Install & load ggplot2
library("ggplot2")
ggplot(iris, aes(Petal.Length, Petal.Width, col = Species)) +  # Graph without transparency
  geom_point(size = 15)

r graph figure 3 change alpha points base r ggplot2

ggplot(iris, aes(Petal.Length, Petal.Width, col = Species)) +  # Transparent graph
  geom_point(size = 15, alpha = 0.3)

r graph figure 4 change alpha points base r ggplot2

Leave a Reply

Your email address will not be published.

Fill out this field
Fill out this field
Please enter a valid email address.
You need to agree with the terms to proceed

Menu
Top