# Coxcomb plots and ‘spiecharts’ in R

**Robin Lovelace - R**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

I was contacted recently by a housing organisation who wanted an attractive visualisation of their finances, arranged in a circular form. Because there were two 4 continuous variables to include, all of which were proportions of each other, the client suggested a plot similar to a pie chart, but with each segment extending out a different radius from the segment. I realised later that what I had been asked to make was a modified coxcomb plot, invented by Florence Nightingale to represent statistics on cause of death during the Crimean War. In fact, I had been asked to make a “spie chart.” This post demonstrates, for the first time to my knowledge, how it can be done using ggplot2. A reproducible example of this, including sample data input, can be found on the project's github repository: https://github.com/Robinlovelace/lilacPlot . Please fork and attribute as appropriate!

# Reading and looking at the data

This is the original dataset I was given:

f <- read.csv("F2.csv") f[1:10, 1:12]

Without worrying too much about the details, the basics of the dataset are as follows:

- One observation per row, these will later be bars on the box plot
- Two components of data - captital and revenue
- Different orders of magnitude: some data is in absolute monetary terms, some in percentages

Base on the above points, a prerequisite was to create preliminary plots and manipulate the data so it would better fit in a coxcomb plot.

The first stage, however, is to demonstrate how the addition of
`coord_polar`

to a barchart can conver it into a pie chart:

(p <- ggplot(f, aes(x = H, y = Allocation)) + geom_bar(color = "black", stat = "identity", width = 1))

p + coord_polar()

The above example works well, but notice that all the bars are of equal widths.
What we want is to be proportional to a value (variable "Value") of each observation.
To do this we use the age-old function `cumsum`

, as described in an
answer to a stackexchange question.

w <- f$Value pos <- 0.5 * (cumsum(w) + cumsum(c(0, w[-length(w)]))) (p <- ggplot(f, aes(x = pos)) + geom_bar(aes(y = Allocation), width = w, color = "black", stat = "identity"))

p + coord_polar(theta = "x") + scale_x_continuous(labels = f$H, breaks = pos)

Finally a spie chart has been created. After that revelation, it was essentially about adding the 'bells and whistles', including a 10% line to represent how much more or less than their share each observation was paying.

# Adding the 10 %

f$Deposit/f$Value ## [1] 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 ## [18] 0.1 0.1 0.1 # add 10% in there p <- ggplot(f) p + geom_bar(aes(x = pos, y = Allocation), width = w, color = "black", stat = "identity") + geom_bar(aes(x = pos, y = 0.1), width = w, color = "black", stat = "identity", fill = "green") + coord_polar()

# make proportional to area f$Allo <- sqrt(f$Allocation) p <- ggplot(f) p + geom_bar(aes(x = pos, y = Allo, width = w), color = "black", stat = "identity") + geom_bar(aes(x = pos, y = sqrt(0.1), width = w), color = "black", stat = "identity", fill = "green") + coord_polar()

# add capital capital <- (f$Captial + f$Deposit)/(f$Value) * f$Allocation capital <- sqrt(capital) p + geom_bar(aes(x = pos, y = Allo, width = w), color = "black", stat = "identity") + geom_bar(aes(x = pos, y = capital, width = w), color = "black", stat = "identity", fill = "red") + geom_bar(aes(x = pos, y = sqrt(0.1), width = w), color = "black", stat = "identity", fill = "green") + coord_polar() + scale_x_continuous(labels = f$H, breaks = pos)

# add ablines p + geom_bar(aes(x = pos, y = Allo, width = w), color = "grey40", stat = "identity", fill = "lightgrey") + geom_bar(aes(x = pos, y = capital, width = w), color = "grey40", stat = "identity", fill = "red") + geom_bar(aes(x = pos, y = sqrt(0.1), width = w), color = "grey40", stat = "identity", fill = "green") + geom_abline(intercept = 1, slope = 0, linetype = 2) + geom_abline(intercept = sqrt(1.1), slope = 0, linetype = 3) + geom_abline(intercept = sqrt(0.9), slope = 0, linetype = 3)

# calculate vertical ablines of divisions v1 <- 0.51 * f$Value[1] v2 <- cumsum(f$Value)[17] + f$Value[18] * 0.31 v3 <- cumsum(f$Value)[17] + f$Value[18] * 0.64 p + geom_bar(aes(x = pos, y = Allo, width = w), color = "grey40", stat = "identity", fill = "lightgrey") + geom_vline(x = v1, linetype = 5) + geom_vline(x = v2, linetype = 5) + geom_vline(x = v3, linetype = 5) + coord_polar()

# putting it all together p <- ggplot(f) p + geom_bar(aes(x = pos, y = Allo, width = w), color = "grey40", stat = "identity", fill = "lightgrey") + geom_bar(aes(x = pos, y = capital, width = w), color = "grey40", stat = "identity", fill = "red") + geom_bar(aes(x = pos, y = sqrt(0.1), width = w), color = "grey40", stat = "identity", fill = "green") + geom_abline(intercept = 1, slope = 0, linetype = 2) + geom_abline(intercept = sqrt(1.1), slope = 0, linetype = 3) + geom_abline(intercept = sqrt(0.9), slope = 0, linetype = 3) + geom_vline(x = v1, linetype = 5) + geom_vline(x = v2, linetype = 5) + geom_vline(x = v3, linetype = 5) + coord_polar() + scale_x_continuous(labels = f$H, breaks = pos) + theme_classic()

The above looks great, but ideally, for an 'infographic' feel, it would have no annoying axes clogging up the visuals. This was done by creating an entirely new ggpot theme.

# Create theme with no axes

theme_infog <- theme_classic() + theme(axis.line = element_blank(), axis.title = element_blank(), axis.ticks = element_blank(), axis.text.y = element_blank()) last_plot() + theme_infog

# Creating a ring

To add the revenue element to the graph is not a task to be taken likely. This was how I tackled the problem, by creating a tall, variable-width bar chart first, and later adding the original spie chart after:

f$Cap.r <- f$Cap/mean(f$Cap) * 0.1 + 1.2 f$Cont.r <- f$Contribution/mean(f$Cap) * 0.1 + 1.2 f$Rep.r <- f$Cont.r + f$Repayments/mean(f$Cap) * 0.1 f$H <- c("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t") p <- ggplot(f) p + geom_bar(aes(x = pos, y = Allo, width = w), color = "grey40", stat = "identity", fill = "lightgrey")

# we need the axes to be bigger for starters - try 1.3 to 1.5 p + geom_bar(aes(x = pos, y = Cap.r, width = w), color = "grey40", stat = "identity", fill = "white") + geom_bar(aes(x = pos, y = Rep.r, width = w), color = "grey40", stat = "identity", fill = "grey80") + geom_bar(aes(x = pos, y = Cont.r, width = w), color = "grey40", stat = "identity", fill = "grey30") + geom_bar(aes(x = pos, y = 1.196, width = w), color = "white", stat = "identity", fill = "white")

last_plot() + geom_bar(aes(x = pos, y = Allo, width = w), color = "grey40", stat = "identity", fill = "grey80") + geom_bar(aes(x = pos, y = capital, width = w), color = "grey40", stat = "identity", fill = "grey30") + geom_bar(aes(x = pos, y = sqrt(0.1), width = w), color = "grey40", stat = "identity", fill = "black") + geom_abline(intercept = 1, slope = 0, linetype = 5) + geom_abline(intercept = sqrt(1.1), slope = 0, linetype = 3) + geom_abline(intercept = sqrt(0.9), slope = 0, linetype = 3) + coord_polar() + scale_x_continuous(labels = f$H, breaks = pos) + theme_infog

# Just inner

After all that it was decided it looked nicer with only the inner ring anyway. Here is the finished product:

p <- ggplot(f) p + geom_bar(aes(x = pos, y = Allo, width = w), color = "grey40", stat = "identity", fill = "grey80") + geom_bar(aes(x = pos, y = capital, width = w), color = "grey40", stat = "identity", fill = "grey30") + geom_bar(aes(x = pos, y = sqrt(0.1), width = w), color = "grey40", stat = "identity", fill = "black") + geom_abline(intercept = 1, slope = 0, linetype = 5) + geom_abline(intercept = sqrt(1.1), slope = 0, linetype = 3) + geom_abline(intercept = sqrt(0.9), slope = 0, linetype = 3) + coord_polar() + scale_x_continuous(labels = f$H, breaks = pos) + theme_infog

ggsave("just-inner.png", width = 7, height = 7, dpi = 800)

**leave a comment**for the author, please follow the link and comment on their blog:

**Robin Lovelace - R**.

R-bloggers.com offers

**daily e-mail updates**about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.