polar area chart

R code of the ggplot2 example

library(ggplot2)
library(dplyr)
library(tidyr)
library(HistData)

## Nightingale's first year, April 1854 to March 1855. The wedges overlap, as
## in her diagram: the largest is drawn first, so that none hides another.
year1 <- Nightingale |>
  filter(Date < as.Date("1855-04-01")) |>
  mutate(Month = factor(as.character(Month), levels = unique(as.character(Month)))) |>
  select(Month, Disease = Disease.rate, Wounds = Wounds.rate, Other = Other.rate) |>
  pivot_longer(-Month, names_to = "cause", values_to = "rate") |>
  mutate(cause = factor(cause, levels = c("Disease", "Wounds", "Other"))) |>
  arrange(desc(rate)) |>
  mutate(order = row_number())
## Two values read out: disease in January, other causes in March.
jan <- year1$rate[year1$Month == "Jan" & year1$cause == "Disease"]
mar <- year1$rate[year1$Month == "Mar" & year1$cause == "Other"]

## A square-root scale makes the area of each wedge, not its radius,
## proportional to the rate, as Nightingale drew it.
## Months as numbers (April = 1, March = 12) so the March label can sit in the
## empty April-June wedges: past 12.5 the angle wraps round to April, and the
## arrow crosses the March/April boundary instead of circling the whole chart.
months <- levels(year1$Month)
p <- ggplot(year1, aes(x = as.integer(Month), y = rate, fill = cause, group = order)) +
  geom_col(width = 1, position = "identity", colour = "white", linewidth = 0.2, alpha = 0.9) +
  annotate("text", x = 10, y = jan / 2, label = lex_number(round(jan)), size = 3,
           colour = "white", fontface = "bold") +
  annotate("segment", x = 13.7, xend = 12.2, y = 200, yend = mar + 8, colour = "#535353",
           linewidth = 0.3, arrow = grid::arrow(length = unit(1.2, "mm"), type = "closed")) +
  annotate("text", x = 14, y = 220, label = paste("Other:", round(mar)), hjust = 0, size = 3,
           colour = "#535353") +
  coord_polar() +
  scale_x_continuous(limits = c(0.5, 12.5), breaks = 1:12, labels = months, oob = scales::oob_keep) +
  scale_y_sqrt(breaks = NULL) +
  labs(title = "Disease killed far more soldiers than wounds",
       subtitle = "British army in the East, April 1854 to March 1855; overlapping wedges, each from the centre, area: deaths per 1\u2009000 soldiers per year",
       x = NULL, y = NULL, fill = NULL,
       caption = "Data: Nightingale 1858, via the HistData R package") +
  theme_lex_viz(grid = "", arrows = "") +
  theme(legend.position = "right")