A **boxplot** is a type of plot that allows us to visualize the five number summary of a variable, which includes:

- The minimum
- The first quartile
- The median
- The third quartile
- The maximum

By knowing these five values, we can gain a strong understanding of the distribution of values in a particular variable.

The easiest way to create a boxplot in R is by using the **geom_boxplot()** function from the **ggplot2** package.

Often when using the **geom_boxplot()** function you may wish to adjust the width of the actual boxplot.

You can use the following basic syntax to do so:

library(ggplot2) ggplot(mtcars, aes(y=mpg)) + geom_boxplot(width=0.5) + xlim(-1,1)

This particular example creates a boxplot of the variable **mpg** from the **mtcars** dataset and specifies that the width of the boxplot should be **0.5**.

We also use the **xlim()** argument to specify the lower and upper limits of the x-axis.

Note that we must include the **xlim()** argument as well or else the width argument in **geom_boxplot()** will not modify the width shown in the plot.

The following example shows how to adjust the width of a boxplot created using the **geom_boxplot****()** function to from ggplot2 in practice.

**Note**: You may first need to install the **ggplot2** package to be able to use the various plotting functions in it. You can use the following syntax to do so:

install.packages('ggplot2')

Once you have this package installed, you can use the functions from it without receiving any errors.

**Example: How to Specify Width in geom_boxplot in ggplot2**

For this particular example, we will use the built-in mtcars dataset in R.

We can use the **head()** function to view the first six rows of this dataset:

#view first six rows of mtcars dataset head(mtcars) mpg cyl disp hp drat wt qsec vs am gear carb Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1

The dataset contains several variables that tell us different information about various cars.

Suppose that we would like to create a boxplot of the **mpg** variable, which represents the miles per gallon of each car in the dataset.

We can use the following syntax to do so:

library(ggplot2) #create boxplot of mpg ggplot(mtcars, aes(y=mpg)) + geom_boxplot() + ggtitle('Boxplot of mpg')

This produces the following boxplot:

The y-axis displays the distribution of values for the **mpg** variable.

Notice that the boxplot currently takes up the entire width of the x-axis.

To make this width thinner, we can use the following syntax:

library(ggplot2) #create boxplot of mpg with thinner width ggplot(mtcars, aes(y=mpg)) + geom_boxplot(width=0.5) + xlim(-1,1)

This produces the following boxplot:

Notice that the width of the boxplot is much thinner now.

Feel free to play around with the values for **width** and **xlim()** to create a boxplot with the exact width that you would like.

**Additional Resources**

The following tutorials explain how to perform other common tasks in ggplot2:

How to Create a Density Plot with ggplot2

How to Adjust Space Between Bars in ggplot2

How to Remove NAs from Plot in ggplot2

How to Change Colors of Bars in Stacked Bart Chart in ggplot2