How can you arrange multiple visualizations on a page with the gridExtra package?

1 Install and load gridExtra

To use the gridExtra package, you need to install it from CRAN and load it into your R session. You can do this with the following code:

install.packages("gridExtra")
library(gridExtra)        

You may also need to load other packages that you use to create your plots, such as ggplot2, lattice, or base graphics.

2 Create some plots

For this example, let's create four plots using ggplot2, based on the mtcars dataset. The first plot shows the relationship between miles per gallon and horsepower, the second plot shows the distribution of miles per gallon by number of cylinders, the third plot shows the distribution of horsepower by number of gears, and the fourth plot shows the scatterplot matrix of four variables.

library(ggplot2)
p1 <- ggplot(mtcars, aes(x = hp, y = mpg)) + geom_point()
p2 <- ggplot(mtcars, aes(x = mpg, fill = factor(cyl))) + geom_histogram()
p3 <- ggplot(mtcars, aes(x = hp, fill = factor(gear))) + geom_density(alpha = 0.5)
p4 <- ggpairs(mtcars[, c("mpg", "hp", "wt", "qsec")])        

3 Arrange plots on a page

The grid.arrange function allows you to arrange multiple plots on a page, either in a matrix layout or a nested layout. You can specify the number of rows and columns, the order of the plots, the widths and heights of the cells, and the margins and spacing between the plots.

For example, to arrange the four plots in a 2 by 2 matrix, you can use this code: grid.arrange(p1, p2, p3, p4, nrow = 2, ncol = 2) To arrange the four plots in a nested layout, where the first plot occupies the left half of the page and the other three plots are stacked on the right half, you can use this code: grid.arrange(p1, arrangeGrob(p2, p3, p4, ncol = 1), ncol = 2) The arrangeGrob function creates a grob object, which is a graphical object that can be manipulated by grid functions. You can also use arrangeGrob to add titles, labels, or legends to your plots.

4 Add annotations to plots

The gridExtra package also provides some functions to add annotations to your plots, such as grid.table, grid.text, and grid.legend. These functions create grob objects that can be placed on the page using grid.arrange or arrangeGrob.

For example, to add a table of summary statistics below the first plot, you can use this code:

library(dplyr)
summary <- mtcars %>% group_by(cyl) %>% summarise(mean_mpg = mean(mpg), sd_mpg = sd(mpg))
t1 <- grid.table(summary)
grid.arrange(p1, t1, ncol = 1, heights = c(3, 1))        

To add a text annotation above the second plot, you can use this code:

t2 <- grid.text("Histogram of mpg by cyl", y = 1.1)
grid.arrange(t2, p2, ncol = 1)        

To add a common legend for the third and fourth plots, you can use this code:

l1 <- grid.legend(grobs = list(p3, p4), x = 0.5, y = -0.1)
grid.arrange(arrangeGrob(p3, p4, ncol = 2), l1, ncol = 1)        

The gridExtra package is a handy tool for arranging and annotating multiple visualizations on a page. You can use it to create complex and customized layouts that showcase your data analysis and storytelling skills.