Draw ggplot2 Plot of Data Frame Subset in R (3 Examples)

 

In this tutorial you’ll learn how to create a ggplot2 plot of a data frame subset in R.

The content of the page is structured as follows:

Here’s the step-by-step process:

 

Example Data, Packages & Default Graph

The following data is used as basement for this tutorial:

data <- data.frame(x = 1:10,                       # Create example data
                   y = 11:20,
                   group = LETTERS[1:2])
data                                               # Print example data
#     x  y group
# 1   1 11     A
# 2   2 12     B
# 3   3 13     A
# 4   4 14     B
# 5   5 15     A
# 6   6 16     B
# 7   7 17     A
# 8   8 18     B
# 9   9 19     A
# 10 10 20     B

The previous output of the RStudio console shows that the example data has ten rows and three columns. The variables x and y contain numeric values and the variable group contains a grouping indicator.

If we want to apply the functions of the ggplot2 package, we also have to install and load ggplot2:

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

Now, we can plot our data as shown below:

ggplot(data, aes(x, y)) +                          # Draw all data in ggplot2 plot
  geom_point()

 

r graph figure 1 draw ggplot2 data frame subset r

 

As shown in Figure 1, the previous R programming syntax created a ggplot2 scatterplot showing the data points of our entire data frame.

 

Example 1: Creating ggplot2 Plot of Data Frame Subset Using Square Brackets

This example shows how to draw a data frame subset in a ggplot2 plot by using square brackets and the %in% operator to subset our data frame by logical condition in R.

Have a look at the following R syntax:

ggplot(data[data$group %in% "A", ], aes(x, y)) +   # Draw only subset of data
  geom_point()

 

r graph figure 2 draw ggplot2 data frame subset r

 

As shown in Figure 2, the previous R programming syntax created a ggplot2 plot that shows only one of the two groups contained in our data frame.

 

Example 2: Creating ggplot2 Plot of Data Frame Subset Using subset() Function

Alternatively to square brackets (as shown in Example 1), we can also use the subset function before drawing our data:

ggplot(subset(data, group %in% "A"), aes(x, y)) +  # Apply subset function
  geom_point()

 

r graph figure 3 draw ggplot2 data frame subset r

 

As shown in Figure 3, the previous R code plotted exactly the same ggplot2 graph as the R code of Example 1.

 

Example 3: Create Data Frame Subset Before Plotting

Another alternative is that we create a data frame subset in the forefront of drawing our plot.

In step 1, we construct a new data frame…

data_subset <- data[data$group %in% "A", ]         # Extract certain rows of data frame

…and in step 2, we create a plot based on the previously created data:

ggplot(data_subset, aes(x, y)) +                   # Using reduced data frame in plot
  geom_point()

 

r graph figure 4 draw ggplot2 data frame subset r

 

As you can see in Figure 4, the previous syntax also created the same plot as in the previous examples.

 

Video, Further Resources & Summary

Do you need more information on the content of this tutorial? Then you might watch the following video of my YouTube channel. In the video, I explain the R codes of this article in RStudio.

 

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In addition, you might want to read the related articles on my website. I have released several posts about similar topics such as variables, graphics in R, regression models, and dates.

 

This tutorial explained how to draw only selected rows of a data frame in a ggplot2 graphic in R programming. Don’t hesitate to let me know in the comments, in case you have further questions.

 

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