ggplot Donut chart

Question

Hi I really have googled this a lot without any joy. Would be happy to get a reference to a website if it exists. I'm struggling to understand the Hadley documentation on polar coordinates and I know that pie/donut charts are considered inherently evil.

That said, what I'm trying to do is

1. Create a donut/ring chart (so a pie with an empty middle) like the tikz ring chart shown here
2. Add a second layer circle on top (with alpha=0.5 or so) that shows a second (comparable) variable.

Why? I'm looking to show financial information. The first ring is costs (broken down) and the second is total income. The idea is then to add + facet=period for each review period to show the trend in both revenues and expenses and the growth in both.

Any thoughts would be most appreciated

Note: Completely arbitrarily if an MWE is needed if this was tried with

donut_data=iris[,2:4]
revenue_data=iris[,1]
facet=iris$Species

That would be similar to what I'm trying to do.. Thanks

Answer 1

Just trying to solve question 2 with the same approach from bdemarest's answer. Also using his code as a scaffold. I added some tests to make it more complete but feel free to remove them.

library(broom)
library(tidyverse)
# Create test data.
dat = data.frame(count=c(10,60,20,50),
                 ring=c("A", "A","B","B"),
                 category=c("C","D","C","D"))

# compute pvalue
cs.pvalue <- dat %>% spread(value = count,key=category) %>%
  ungroup() %>% select(-ring) %>% 
  chisq.test() %>% tidy()
cs.pvalue <- dat %>% spread(value = count,key=category) %>% 
  select(-ring) %>%
  fisher.test() %>% tidy() %>% full_join(cs.pvalue)

# compute fractions
#dat = dat[order(dat$count), ]
dat %<>% group_by(ring) %>% mutate(fraction = count / sum(count),
                                      ymax = cumsum(fraction),
                                      ymin = c(0,ymax[1:length(ymax)-1]))


# Add x limits
baseNum <- 4
#numCat <- length(unique(dat$ring))
dat$xmax <- as.numeric(dat$ring) + baseNum
dat$xmin = dat$xmax -1


# plot
p2 = ggplot(dat, aes(fill=category,
                     alpha = ring,
                     ymax=ymax, 
                     ymin=ymin, 
                     xmax=xmax, 
                     xmin=xmin)) +
  geom_rect(colour="grey30") +
  coord_polar(theta="y") +
  geom_text(inherit.aes = F,
            x=c(-1,1),
            y=0,
            data = cs.pvalue,aes(label = paste(method,
                                               "\n",
                                               format(p.value,
                                                      scientific = T,
                                                      digits = 2))))+
  xlim(c(0, 6)) +
  theme_bw() +
  theme(panel.grid=element_blank()) +
  theme(axis.text=element_blank()) +
  theme(axis.ticks=element_blank(),
        panel.border = element_blank()) +
  labs(title="Customized ring plot") + 
  scale_fill_brewer(palette = "Set1") +
  scale_alpha_discrete(range = c(0.5,0.9))

p2

And the result: