Arranging subplots with ggplot2

For my recently published paper, I produced not-so-standard figures that show the two step decomposition used in the analysis. Have a look:

fig1
Figure 3 from my paper (PDF)

Actually, ggplot2 is a very powerful and flexible tool that allows to draw figures with quite a complex layout. Today I want to show the code that aligns six square plots (actually, maps) just as in the figure above. And it’s all about the handy function ggplot2::annotation_custom(). Since I used the layout more than once, I wrapped the code that produced it into a function that takes a list of 6 square plots as an input and yields the arranged figure with arrows as an output. Here is the commented code of the function.

align_six_plots <- function(list.plots, 
                                    family = "",
                                    labels=LETTERS[1:6], 
                                    labels.size=8){

        require(tidyverse)
        require(gridExtra)

        gg <- ggplot()+
                coord_equal(xlim = c(0, 21), ylim = c(0, 30), expand = c(0,0))+

                annotation_custom(ggplotGrob(list.plots[[1]]),
                                  xmin = 0.5, xmax = 8.5, ymin = 21, ymax = 29)+

                annotation_custom(ggplotGrob(list.plots[[2]]),
                                  xmin = 12.5, xmax = 20.5, ymin = 19.5, ymax = 27.5)+
                annotation_custom(ggplotGrob(list.plots[[3]]),
                                  xmin = 12.5,xmax = 20.5,ymin = 10.5,ymax = 18.5)+

                annotation_custom(ggplotGrob(list.plots[[4]]),
                                  xmin = 0.5, xmax = 8.5, ymin = 9,ymax = 17)+
                annotation_custom(ggplotGrob(list.plots[[5]]),
                                  xmin = 0.5, xmax = 8.5, ymin = 0, ymax = 8)+
                annotation_custom(ggplotGrob(list.plots[[6]]),
                                  xmin = 12.5,xmax = 20.5, ymin = 0, ymax = 8)+

                labs(x = NULL, y = NULL)+
                theme_void()


        # DF with the coordinates of the 5 arrows
        df.arrows <- data.frame(id=1:5,
                                x=c(8.5,8.5,12.5,12.5,12.5),
                                y=c(21,21,10.5,10.5,10.5),
                                xend=c(12.5,12.5,8.5,8.5,12.5),
                                yend=c(20.5,17.5,10,7,7))

        # add arrows
        gg <- gg +
                geom_curve(data = df.arrows %>% filter(id==1),
                           aes(x=x,y=y,xend=xend,yend=yend),
                           curvature = 0.1,
                           arrow = arrow(type="closed",length = unit(0.25,"cm"))) +
                geom_curve(data = df.arrows %>% filter(id==2),
                           aes(x=x,y=y,xend=xend,yend=yend),
                           curvature = -0.1,
                           arrow = arrow(type="closed",length = unit(0.25,"cm"))) +
                geom_curve(data = df.arrows %>% filter(id==3),
                           aes(x=x,y=y,xend=xend,yend=yend),
                           curvature = -0.15,
                           arrow = arrow(type="closed",length = unit(0.25,"cm"))) +
                geom_curve(data = df.arrows %>% filter(id==4),
                           aes(x=x,y=y,xend=xend,yend=yend),
                           curvature = 0,
                           arrow = arrow(type="closed",length = unit(0.25,"cm"))) +
                geom_curve(data = df.arrows %>% filter(id==5),
                           aes(x=x,y=y,xend=xend,yend=yend),
                           curvature = 0.3,
                           arrow = arrow(type="closed",length = unit(0.25,"cm")))

        # add labes
        gg <- gg + annotate('text',label = labels,
                            x=c(.5,12.5,12.5,.5,.5,12.5)+.5,
                            y=c(29,27.5,18.5,17,8,8)+.1,
                            size=labels.size,hjust=0, vjust=0, family = family)

        return(gg)
}

Let’s check, if the function works. For that I create just a blank plot, clone it six times, store the six plots in a list, and finally feed it to the function.

library(tidyverse)
library(ggthemes)

# create a simple blank square plot
p <- ggplot()+
  expand_limits(x = c(0,1), y = c(0,1))+
  theme_map()+
  theme(panel.border = element_rect(color = "black", size = 0.5, fill = NA),
        aspect.ratio = 1)

# clone this plot six times and store as a list of six
plots <- mget(rep("p", 6))

# use the function on the list
six <- align_six_plots(plots)

# save the output
ggsave("six_square_plots_aligned.png", six, width=12, height=18)

fig2

Just what we wanted to get.

To reproduce all the actual results and figures from my paper, have a look at this github repo.