Print ggplot2 Plot within for-Loop in R (Example)

In this article you’ll learn how to draw ggplot2 plots within a for-loop in the R programming language.

The post looks as follows:

• Introducing Example Data
• Example: Plotting ggplot2 Plots within Loop
• Video, Further Resources & Summary

You’re here for the answer, so let’s get straight to the programming part…

Introducing Example Data

We will use the following data as basement for the example of this R programming tutorial:

set.seed(159159)                                      # Create example data
data <- data.frame(x = 1:100,
                   y1 = rnorm(100),
                   y2 = rnorm(100),
                   y3 = rnorm(100))

Our example data contains 100 rows and four columns. The variable x is ranging from 1 to 100 and the columns y1, y2, and y2 contain 100 random normally distributed numbers each.

We also need to install and load the ggplot2 add-on package to RStudio:

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

Now, we can draw a basic ggplot2 graph as follows:

ggplot(data, aes(x = x, y = y1)) +                    # Basic ggplot2 plot of x & y1
  geom_point()

Figure 1: Basic Scatterplot Created by ggplot2 Package.

In Figure 1, you can see the result of the previous R code: A scatterplot of x and y1.

Now, let’s assume we want to create a ggplot2 plot of each combination of x and y1, y2, and y3 respectively. In such a scenario, we may want to use a for-loop:

for(i in 2:ncol(data)) {                              # ggplot within for-loop
  ggplot(data, aes(x = x, y = data[ , i])) +
    geom_point()
  Sys.sleep(2)
}

Damn! No graphic was returned!

So why does ggplot2 not work if it is inside a for-loop although it works outside of it?!

That’s what I’m going to show you next…

Example: Plotting ggplot2 Plots within Loop

If we want to draw a plot within a for-loop, we need to wrap the print function around the R code creating the plot. Have a look at the following R syntax:

for(i in 2:ncol(data)) {                              # Printing ggplot within for-loop
  print(ggplot(data, aes(x = x, y = data[ , i])) +
          geom_point())
  Sys.sleep(2)
}

Figure 2: Showing ggplot2 Plots within for-Loop using print() Function.

After running the previous R code, you will see three ggplot2 graphs popping up at the bottom right of RStudio with a delay of 2 seconds.

Looks good!

Video, Further Resources & Summary

Would you like to know more about the ggplot2 package in R? Then you could watch the following video of my YouTube channel. In the video, I explain the R codes of this article in RStudio:

Furthermore, you might have a look at the related articles of this website. A selection of articles can be found here.

• R Graphics Gallery
• The R Programming Language

This tutorial illustrated how to use the ggplot2 package within while- or for-loops in R. Don’t hesitate to let me know in the comments, in case you have additional questions. In addition, please subscribe to my email newsletter in order to receive updates on the newest articles.