Draw Plot with two Y-Axes in R

In this article, we are going to discuss how to create y-axes of both sides of a plot in R programming language.

Sometimes for quick data analysis, it is required to create a single graph having two data variables with different scales. To do that in R language we use the following steps.

First, we create a sample data, such that the sample data consists of three numeric vectors: x, y1, and y2. The x data will determine X-axis information whereas y1 and y2 will be used for two Y-Axis simultaneously.

Now, we will create a scatter plot with two different colors and y-axis values on the left and right sides of the plot. To do so, firstly we will create white space around the plot. This leave space for second y-axis. This can be done using par() method. Now, create the first plot (i.e. the red cross dots) around the first Y-Axis that takes into account data y1.

Syntax:

plot(x, y1, pch , col )

 Next, set new to TRUE in par() method. This needs to be called again after the first plot has been created. This tells the plot that a new plot will be drawn over the first one.

Syntax:

par(new = TRUE)

 Next, plot the second plot now with taking y2 data in account.

Syntax:

plot(x, y2, pch = 15, col = 3, axes = FALSE, xlab = “”, ylab = “”) 

Next set axis or any additional attribute if required.

Example:

# Create sample data
set.seed(2585)                           

x <- rnorm(45)
y1 <- x + rnorm(45)
y2 <- x + rnorm(45, 7)

# Draw first plot using axis y1
par(mar = c(7, 3, 5, 4) + 0.3)              
plot(x, y1, pch = 13, col = 2)  

# set parameter new=True for a new axis
par(new = TRUE)         

# Draw second plot using axis y2
plot(x, y2, pch = 15, col = 3, axes = FALSE, xlab = "", ylab = "")

axis(side = 4, at = pretty(range(y2)))      
mtext("y2", side = 4, line = 3)             

Output:

Example 2:

# Create sample data
                          
x <- c(1,2,3,4,5,6,7,8,9,10)
y1 <-c(2,5,2,8,6,8,3,4,2,4)
y2 <-c(2,5,3,7,5,9,7,9,4,1)

# Draw first plot using axis y1
par(mar = c(7, 3, 5, 4) + 0.3)              
plot(x, y1, type="l", col = 2)  

# set parameter new=True for a new axis
par(new = TRUE)         

# Draw second plot using axis y2
plot(x, y2, type="l", col = 3, axes = FALSE, xlab = "", ylab = "")

axis(side = 4, at = pretty(range(y2)))      
mtext("y2", side = 4, line = 3)

Output: