Fill Area Under Line Plot in R (2 Examples)

In this post you’ll learn how to add a filling color below the line in a line graph in R programming.

The tutorial looks as follows:

Let’s jump right to the R syntax!

Creating Example Data

Consider the following example data:

data <- data.frame(x = 1:6,         # Create example data frame
                   y = c(2, 5, 6, 3, 5, 4))
data                                # Print example data frame

As you can see based on Table 1, our exemplifying data is a data frame consisting of six rows and two variables.

Example 1: Fill Area Under Line Plot Using Base R

Example 1 illustrates how to draw a Base R line graph with a filling color below the line.

Let’s first create a line plot without filling color:

plot(data, type = "l")              # Draw Base R line plot without filled area

By running the previous R code, we have created Figure 1, i.e. a Base R line graphic without filling color.

Let’s add some color to the area under the line!

To accomplish this, we can use the polygon function as shown below:

plot(data, type = "l")              # Fill area below line
polygon(x = c(min(data$x), data$x, max(data$x)),
        y = c(0, data$y, 0),
        col = "#1b98e0")

As shown in Figure 2, we have created a Base R line plot with color under the line curve.

Example 2: Fill Area Under Line Plot Using ggplot2 Package

In Example 2, I’ll illustrate how to add color below the line of a ggplot2 graphic.

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

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

Next, let’s draw a ggplot2 plot without colors:

ggp <- ggplot(data, aes(x, y)) +    # Draw ggplot2 line plot without filled area
  geom_line()
ggp

Figure 3 illustrates the output of the previous code – A ggplot2 plot without filling color.

Now, we can add color to the graph using the geom_area function:

ggp +                               # Fill area below line
  geom_area(fill = "#1b98e0")

As shown in Figure 4, the previous R code has added some color below the line.

Note: The ggplot2 package changes the y-axis to start at zero when using the geom_area function. This is a difference compared to Base R.

In case you want to keep the y-axis limits, you may use the geom_ribbon function instead:

ggp +                               # Filled area with same y-axis limits
  geom_ribbon(aes(ymin = min(y),
                  ymax = y),
              fill = "#1b98e0")

Video & Further Resources

Have a look at the following video on my YouTube channel. In the video, I’m explaining the R programming code of this article in RStudio.

The YouTube video will be added soon.

In addition, you might want to read the related tutorials on my website. I have released numerous tutorials on topics such as dates, plot legends, lines, and graphics in R:

• Add Grid Line Consistent with Ticks on Axis to Plot
• Draw Vertical Line to X-Axis of Class Date in ggplot2 Plot
• Add Labels at Ends of Lines in ggplot2 Line Plot
• Control Line Color & Type in ggplot2 Plot Legend
• R Graphics Gallery
• All R Programming Examples

In this post you have learned how to change the filling color below the line in a line plot in the R programming language. In case you have further comments or questions, let me know in the comments section below.