This recipe shows you how to get control over an axis within a ggplot plot.
The ggplot2 package does a great job of automatically setting the appearance of the axes, but sometimes, even in the early stages of your project, you may want your axis to appear in a specific shape, showing, for instance, a defined number of tickmarks.
This is what this recipe is all about—giving you control over the appearance of your ggplot axes.
In this example, we will use a plot based on the Iris dataset.
The Iris dataset is one of most used datasets in R tutorials and learning sessions, and it is derived from a 1936 paper by Ronald Fisher, named The use of multiple measurements in taxonomic problems.
Data was observed on 50 samples of three species of the iris flower:
- Iris setosa
- Iris virginica
- Iris versicolor
On each sample for features were recorded:
- length of the sepals
- width of the sepals
- length of the petals
- width of the petals
For a general and brief introduction to ggplot plots, take a look at the How it works… section of the previous recipe.
The first step needed to get started with this recipe is ggplot2 package installation and loading:
install.packages("ggplot2")
library(ggplot2)After doing that, we will be able to create a ggplot2 plot to work on in this recipe:
plot <- ggplot(data = iris, aes(x = Sepal.Length, y = Sepal.Width)) + geom_point()
- Set axis range from 0 to 10.
Using the
expand_limits()function, we can set the origin and the end of the x and y axes, passing these values in two different vectors, one for the x and one for the y argument of theexpand_limits()function:plot <- plot + expand_limits(x = c(0,10),y = c(0,10))
This will result in setting the range of the x and y axes from 0 to 10.
.
By displaying predetermined tick marks,
ggplotautomatically defines a convenient number of tick marks, working this out with its own internal algorithms. However, you can force the plot to have a custom number of algorithms using thescale_y_continuos()andscale_x_continuos()functions, passing a vector with the desired breaks to thebreaksargument:plot <- plot + scale_y_continuous(breaks = c(0,5,10))
This piece of code, for instance, will result in a plot having tick marks only on 0, 5, and 10:
- Hide the tick marks:
plot <- plot + scale_y_continuous(breaks = NULL) + scale_x_continuous(breaks = NULL)
- Set a fixed ratio between x and y axes:
plot <- plot + coord_fixed(ratio = 4/3)
It feels like some kind of pop art, doesn't it?
So, you are now a ggplot artist, congratulations!