In this article, I will show you how to use the
ggplot2 plotting library in R. It was written by Hadley Wickham. If you don’t have already have it, install it and load it up:
qplot is the quickest way to get off the ground running. For this demonstration, we will use the
mtcars dataset from the
library(datasets) qplot(mpg, disp, data = mtcars)
We can also color the datapoints based on the number of cylinders that each car has as follows:
mtcars$cyl <- as.factor(mtcars$cyl) qplot(mpg, disp, data = mtcars, color = cyl)
You can also plot a histogram:
qplot(mtcars$mpg, fill = mtcars$cyl, binwidth = 2)
Another thing you may notice is that instead of specifying
data = mtcars, I just used
mtcars$cyl here. Both are acceptable ways, and you are free to use whichever you prefer.
You can also split the plot using facets.
qplot(mpg, disp, data = mtcars, facets = cyl ~ .)
You can also split along both the x axes and y axes as follows:
mtcars$gear <- as.factor(mtcars$gear) qplot(mpg, disp, data - mtcars, facets = cyl ~ gear)
qplot is a great way to get off the ground running, it does not provide the same level of customization as
ggplot. All the above plots can be reproduced using
ggplot as follows:
ggplot(mtcars, aes(mpg, disp)) + geom_point() ggplot(mtcars, aes(mpg, disp)) + geom_point(aes(color = cyl) ggplot(mtcars, aes(mpg)) + geom_bar(aes(fill = cyl), binwidth = 2) ggplot(mtcars, aes(mpg, disp)) + geom_point() + facet_grid(cyl ~ .) ggplot(mtcars, aes(mpg, disp)) + geom_point() + facet_grid(cyl ~ gear)
There are a variety of options available for customization. I will describe a few here.
For example, for the points, we can specify size, color and alpha. Alpha determines how opaque each point is, with 0 being the lowest, and 1 being the highest value it can take.
We can specify the labels for the x axis and y axis using
ylab respectively, and the title using
There are a variety of options for modifying the legend title, text, colors, order, position, etc.
You can also select a theme for the plot. Use
?ggtheme to see all the options that are available.
Here is an example:
ggplot(mtcars, aes(mpg, disp)) + geom_point(aes(color = carb), size = 2.5, alpha = 0.8) + facet_grid(cyl ~ gear) + xlab('Miles per US gallon') + ylab('Displacement in cubic inches') + ggtitle('Fuel consumption vs displacement') + theme(legend.background = element_rect(colour = 'orange', fill = 'purple', size = 1.2, linetype = 'dotted'), legend.key = element_rect(fill = 'pink'), legend.position = 'top')
Please note the spelling of “colour” in the legend settings. “Color” will not work.
The above plot is only for demonstration purposes, and it shows some of the many customization options available in the
ggplot2 library. For more options, please refer to the ggplot2 documentation.
If you have any questions, please feel free to leave a comment or reach out to me on Twitter.