Joining 2 bar columns in barcharts with curved line - r

Question

I have below ggplot:
library(ggplot2)
data = rbind(data.frame('val' = c(10, 30, 15), 'name' = c('A', 'B', 'C'), group = 'gr1'), data.frame('val' = c(30, 40, 12), 'name' = c('A', 'B', 'C'), group = 'gr2'))
ggplot(data, # Draw barplot with grouping & stacking
aes(x = group,
y = val,
fill = name)) +
geom_bar(stat = "identity",
position = "stack", width = .1)
With this, I am getting below plot
However, I want to connect these bars with a curved area where the area would be equal to the value of the corresponding bar-component. A close example could be like,
Is there any way to achieve this with ggplot?
Any pointer will be very helpful.

Answer 1

This is something like an alluvial plot. There are various extension packages that could help you create such a plot, but it is possible to do it in ggplot directly using a bit of data manipulation.
library(tidyverse)
alluvia <- data %>%
group_by(name) %>%
summarize(x = seq(1, 2, 0.01),
val = pnorm(x, 1.5, 0.15) * diff(val) + first(val))
ggplot(data,
aes(x = as.numeric(factor(group)),
y = val,
fill = name)) +
geom_bar(stat = "identity",
position = "stack", width = .1) +
geom_area(data = alluvia, aes(x = x), position = "stack", alpha = 0.5) +
scale_x_continuous(breaks = 1:2, labels = levels(factor(data$group)),
name = "Group", expand = c(0.25, 0.25)) +
scale_fill_brewer(palette = "Set2") +
theme_light(base_size = 20)
EDIT
A more generalized solution for more than 2 groups would be
library(tidyverse)
alluvia <- data %>%
mutate(group = as.numeric(factor(group)),
name = factor(name)) %>%
arrange(group) %>%
group_by(name) %>%
mutate(next_group = lead(group),
next_val = lead(val)) %>%
filter(!is.na(next_val)) %>%
group_by(name, group) %>%
summarise(x = seq(group + 0.01, next_group - 0.01, 0.01),
val = (next_val - val) * pnorm(x, group + 0.5, 0.15) + val)
ggplot(data,
aes(x = as.numeric(factor(group)),
y = val,
fill = name)) +
geom_bar(stat = "identity",
position = "stack", width = .1) +
geom_area(data = alluvia, aes(x = x), position = "stack", alpha = 0.5) +
scale_x_continuous(breaks = seq(length(unique(data$group))),
labels = levels(factor(data$group)),
name = "Group", expand = c(0.25, 0.25)) +
scale_fill_brewer(palette = "Set2") +
theme_light(base_size = 20)