Bar charts connected by lines / How to connect two graphs arranged with grid.arrange in R / ggplot2

Question

At Facebook research, I found these beautiful bar charts which are connected by lines to indicate rank changes:

https://research.fb.com/do-jobs-run-in-families/

I would like to create them using ggplot2. The bar-chart-part was easy:

library(ggplot2)
library(ggpubr)
state1 <- data.frame(state=c(rep("ALABAMA",3), rep("CALIFORNIA",3)), 
                 value=c(61,94,27,10,30,77), 
                 type=rep(c("state","local","fed"),2),
                 cumSum=c(rep(182,3), rep(117,3)))
state2 <- data.frame(state=c(rep("ALABAMA",3), rep("CALIFORNIA",3)), 
                 value=c(10,30,7,61,94,27), 
                 type=rep(c("state","local","fed"),2),
                 cumSum=c(rep(117,3), rep(182,3)))
fill <- c("#40b8d0", "#b2d183", "#F9756D")

p1 <- ggplot(data = state1) +
  geom_bar(aes(x = reorder(state, value), y = value, fill = type), stat="identity") +
  theme_bw() + 
  scale_fill_manual(values=fill) + 
  labs(x="", y="Total budget in 1M$") +
  theme(legend.position="none", 
        legend.direction="horizontal", 
        legend.title = element_blank(),
        axis.line = element_line(size=1, colour = "black"),
        panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
        panel.border = element_blank(), panel.background = element_blank()) +
  coord_flip() 

p2 <- ggplot(data = state2) +
  geom_bar(aes(x = reorder(state, value), y = value, fill = type), stat="identity") +
  theme_bw() + 
  scale_fill_manual(values=fill) + labs(x="", y="Total budget in 1M$") +
  theme(legend.position="none", 
        legend.direction="horizontal", 
        legend.title = element_blank(),
        axis.line = element_line(size=1, colour = "black"),
        panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
        panel.border = element_blank(), 
        panel.background = element_blank()) +
  scale_x_discrete(position = "top") + 
  scale_y_reverse() +
  coord_flip()

p3 <- ggarrange(p1, p2, common.legend = TRUE, legend = "bottom")

But I couldn't come up with a solution to the line-part. When adding lines e.g. to the left side by

p3 + geom_segment(aes(x = rep(1:2, each=3), xend = rep(1:10, each=3), 
                   y = cumSum[order(cumSum)], yend=cumSum[order(cumSum)]+10), size = 1.2)

The problem is that the lines will not be able to cross over to the right side. It looks like this:

Basically, I would like to connect the 'California' bar on the left with the Caifornia bar on the right.

To do that, I think, I have to get access to the superordinate level of the graph somehow. I've looked into viewports and was able to overlay the two bar charts with a chart made out of geom_segment but then I couldn't figure out the right layout for the lines:

subplot <- ggplot(data = state1) + 
  geom_segment(aes(x = rep(1:2, each=3), xend = rep(1:2, each=3), 
                   y = cumSum[order(cumSum)], yend =cumSum[order(cumSum)]+10), 
               size = 1.2)

vp <- viewport(width = 1, height = 1, x = 1, y = unit(0.7, "lines"), 
               just ="right", "bottom"))
print(p3)
print(subplot, vp = vp)

Help or pointers are greatly appreciated.

Answer 1

This is a really interesting problem. I approximated it using the patchwork library, which lets you add ggplots together and gives you an easy way to control their layout—I much prefer it to doing anything grid.arrange-based, and for some things it works better than cowplot.

I expanded on the dataset just to get some more values in the two data frames.

library(tidyverse)
library(patchwork)

set.seed(1017)

state1 <- data_frame(
  state = rep(state.name[1:5], each = 3),
  value = floor(runif(15, 1, 100)),
  type = rep(c("state", "local", "fed"), times = 5)
)

state2 <- data_frame(
  state = rep(state.name[1:5], each = 3),
  value = floor(runif(15, 1, 100)),
  type = rep(c("state", "local", "fed"), times = 5)
)

Then I made a data frame that assigns ranks to each state based on other values in their original data frame (state1 or state2).

ranks <- bind_rows(
  state1 %>% mutate(position = 1),
  state2 %>% mutate(position = 2)
)  %>%
  group_by(position, state) %>%
  summarise(state_total = sum(value)) %>%
  mutate(rank = dense_rank(state_total)) %>%
  ungroup()

I made a quick theme to keep things very minimal and drop axis marks:

theme_min <- function(...) theme_minimal(...) +
  theme(panel.grid = element_blank(), legend.position = "none", axis.title = element_blank())

The bump chart (the middle one) is based on the ranks data frame, and has no labels. Using factors instead of numeric variables for position and rank gave me a little more control over spacing, and lets the ranks line up with discrete 1 through 5 values in a way that will match the state names in the bar charts.

p_ranks <- ggplot(ranks, aes(x = as.factor(position), y = as.factor(rank), group = state)) +
  geom_path() +
  scale_x_discrete(breaks = NULL, expand = expand_scale(add = 0.1)) +
  scale_y_discrete(breaks = NULL) +
  theme_min()
p_ranks

For the left bar chart, I sort the states by value and turn the values negative to point to the left, then give it the same minimal theme:

p_left <- state1 %>%
  mutate(state = as.factor(state) %>% fct_reorder(value, sum)) %>%
  arrange(state) %>%
  mutate(value = value * -1) %>%
  ggplot(aes(x = state, y = value, fill = type)) +
    geom_col(position = "stack") +
    coord_flip() +
    scale_y_continuous(breaks = NULL) +
    theme_min() +
    scale_fill_brewer()
p_left

The right bar chart is pretty much the same, except the values stay positive and I moved the x-axis to the top (becomes right when I flip the coordinates):

p_right <- state2 %>%
  mutate(state = as.factor(state) %>% fct_reorder(value, sum)) %>%
  arrange(state) %>%
  ggplot(aes(x = state, y = value, fill = type)) +
    geom_col(position = "stack") +
    coord_flip() +
    scale_x_discrete(position = "top") +
    scale_y_continuous(breaks = NULL) +
    theme_min() +
    scale_fill_brewer()

Then because I've loaded patchwork, I can add the plots together and specify the layout.

p_left + p_ranks + p_right +
  plot_layout(nrow = 1)

You may want to adjust spacing and margins some more, such as with the expand_scale call with the bump chart. I haven't tried this with axis marks along the y-axes (i.e. bottoms after flipping), but I have a feeling things might get thrown out of whack if you don't add a dummy axis to the ranks. Plenty still to mess around with, but it's a cool visualization project you posed!