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
library("ggplot2")

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() + 
  scale_y_continuous(
    "Kilometers", 
    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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8 Comments. Leave new

  • this kind of two axises represents the same information but difference scales, it is an alternative. In some cases,we want to present two variables in two Y axis respectively, it may be different.

    Reply
  • Lulukapupu
    May 5, 2021 1:30 pm

    Yes, it is very very nice 🙂

    Reply
  • I learn a lot of things here, could you please help me with how to plot the bar chat?
    my data is :
    Month Precipitation_mm Min_temperature _◦C Max_temperature_◦C
    Jan 278.53 21.51 30.43
    Feb 252.62 21.49 30.61
    Mar 293.64 21.62 30.87
    Apr 288.77 21.81 31.11
    May 242.17 21.74 31.13
    Jun 197.26 21.35 30.8
    Jul 171.72 20.97 30.62
    Aug 166.9 20.95 30.84
    Sep 174.87 21.09 31.02
    Oct 222.3 21.39 31.34
    Nov 269.04 21.56 31.16
    Dec 299.19 21.7 30.77

    Thank you so much

    Reply
  • Bir Bikram Biswasray
    May 18, 2022 8:47 am

    Dear Joachim,

    Thanks for this tutorial, is there any way to have two different Y-axis units using ggplot2 with a boxplot? I can get the Y-axis but it comes as the same information as the other Y axis. For example, I want Y1 axis to only have data up to 2000 but Y2 axis up to 8000.

    Warm Regards,

    Bir Bikram Biswasray

    Reply

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