Draw ggplot2 Plot with Two Y-Axes in R (Example) | Different Scale on Each Side


In this R programming tutorial you’ll learn how to return a ggplot2 graph with 2 y-axes and different scales on each side.

Table of contents:

Let’s get started…


Creation of Example Data

We’ll use the following data as basement for this R tutorial.

set.seed(93756)                  # Create example data
x <- rnorm(50)
y <- x + 0.3 * rnorm(50)
data <- data.frame(x, y)
head(data)                       # Head of example data
#            x          y
# 1 -0.6203384 -0.6489154
# 2 -0.7203421 -0.7941812
# 3  2.1730194  2.3723400
# 4  0.2500335 -0.1291261
# 5  0.1308206  0.0727594
# 6 -1.6816844 -2.1235243

The previous output of the RStudio console shows that our example data consists of two numeric columns x and y.


Example: Drawing ggplot2 Plot with Two Y-Axes Using sec_axis() Function

In this Example, I’ll show how to print a ggplot2 graphic that has two y-axes with different scales on each side of the plot.

First, we have to install and load the ggplot2 add-on package:

install.packages("ggplot2")      # Install & load ggplot2 package

Now, we can use the scale_y_continuous & sec_axis axis functions to draw a ggplot2 plot with two y-axes as shown below:

ggplot(data, aes(x, y)) +        # Create ggplot2 plot
  geom_point() + 
    sec.axis = sec_axis(~ . * 1000, name = "Meters")


r graph figure 1 draw ggplot two y axes r


As shown in Figure 1, the previously shown R syntax created a ggplot2 scatterplot.

This plot has two y-axes. The y-axis on the left side of the plot shows the scale in the metric kilometers and on the right side the scale is shown in meters.

Within the sec_axis we had to specify the conversion formula for kilometers and meters (i.e. 1000 meters = 1 kilometer).

Note that in the past there was a longer discussion on Stack Overflow, if features supporting two y-axes should be available for ggplot2 plots in R. In case you are interested in this discussion, you may check out this thread.


Video & Further Resources

Have a look at the following video of the Statistics Globe YouTube channel. I’m explaining how to draw double ggplot2 axes using the R syntax of this tutorial in the video.


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In addition, you could read some of the related articles of this website:


In summary: You learned in this tutorial how to draw a plot with two y-axes using the ggplot2 package in the R programming language. Don’t hesitate to tell me about it in the comments section below, if you have additional questions on dual y-axes or any other topic.


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