Add Regression Line to ggplot2 Plot in R (Example) | Draw Linear Slope to Scatterplot

In this R tutorial you’ll learn how to add regression lines on scatterplots.

The article contains one examples for the addition of a regression slope. More precisely, the content of the tutorial looks as follows:

• Creation of Example Data
• Example 1: Adding Linear Regression Line to Scatterplot
• Video, Further Resources & Summary

With that, let’s start right away.

Creation of Example Data

In the following R programming tutorial, we’ll use the data frame below as basement:

set.seed(8743)                             # Create example data
x <- rnorm(1000)
y <- rnorm(1000) + 0.3 * x
data <- data.frame(x, y)
head(data)                                 # Print first rows of data
#            x          y
# 1  1.2138865 -0.3500503
# 2 -1.8828867 -1.1576045
# 3 -0.2739309 -0.9035707
# 4  1.0028479 -0.1521459
# 5  0.6276009 -0.4914815
# 6 -0.9443908 -1.3845497

As you can see based on the output of the RStudio console, our example data contains two numeric columns x and y.

Furthermore, we have to install and load the ggplot2 package to R:

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

Now, we can draw a basic scatterplot with the ggplot2 package with the ggplot & geom_point functions as follows:

ggp <- ggplot(data, aes(x, y)) +           # Create basic ggplot
  geom_point()
ggp                                        # Print ggplot

Figure 1: Basic ggplot2 Scatterplot without Regression Line.

Figure 1 shows the graphic that we have just created. It’s a simple dotplot showing the correlation of our variables x and y.

Example 1: Adding Linear Regression Line to Scatterplot

As you have seen in Figure 1, our data is correlated. We may want to draw a regression slope on top of our graph to illustrate this correlation.

With the ggplot2 package, we can add a linear regression line with the geom_smooth function. Have a look at the following R code:

ggp +                                      # Add regression line
  geom_smooth(method = "lm",
              formula = y ~ x)

Figure 2: ggplot2 Scatterplot with Linear Regression Line and Variance.

Figure 2 shows our updated plot. As you can see, it consists of the same data points as Figure 1 and in addition it shows the linear regression slope corresponding to our data values. The shaded area around the trend line illustrates the variance.

Video, Further Resources & Summary

Do you want to know more about regression slopes and graphics in R? Then you may watch the following video which I have published on my YouTube channel. In the video, I’m explaining the R programming codes of this tutorial.

Besides the video, you may want to read the other tutorials of my website. You can find some tutorials here.

• Scatterplot in R
• Draw Vertical Line to X-Axis in ggplot2 Plot
• R Graphics Gallery
• The R Programming Language

In summary: In this post, I showed how to insert a linear regression equation line to a ggplot2 graph in R. In case you have any additional questions, let me know in the comments section.