Pie Chart ggplot Style is Surprisingly Hard! Here’s How I Did it

How do you make a pie chart in ggplot2 package in R? It's not that obvious

Pie chart ggplot style is a bad memory for me. I had made pie charts using base R, and it had been no big deal. I also had made time series and other plots with ggplot2, and it was no problem. But when I went to make a pie chart ggplot style for the first time, I found it very confusing!

The situation was my colleague and I had done some research into different types of deeper learning strategies in higher education, and one of them is to have students create types of media. We wanted to have a pie chart displaying the distribution of the types of media that were created in the studies of deeper learning we reviewed. Here are our data:

Type

Percentage

Blog

22%

Digital storytelling

11%

ePortfolio

11%

Podcast

6%

Video

50%

Total

100%

Pie Chart ggplot Style was Much Harder than Base R

As you can imagine, this was supposed to be a very simple project! But it was not. I posted the code on Github for you here. I will show you how I went through it.

First I read in the dataframe I had made from the estimates in the table, and loaded the ggplot2 library.

piechart_df <- readRDS("piechart_df.rds")
library(ggplot2)

If you run piechart_df to look at it, you will see this:

  Proportion                 Type
1 0.22222222                 Blog
2 0.11111111 Digital Storytelling
3 0.11111111           ePortfolio
4 0.05555556              Podcast
5 0.50000000                Video

As you can see, the data are represented in terms of proportions. I also wanted to have customized colors, so I made this color vector called pie_colors to refer to later in my ggplot2 coding.

pie_colors <- c("orangered4","orchid4",
  "palegreen4","paleturquoise4", "palevioletred4")

Pie Chart ggplot Style: There is No “geom_pie” or “geom_circle”

Now, before we look at the code, let me show you the output. This is the final pie chart below.

Of course, I expected there to be a “geom” shape for a circle. There isn’t! It’s geom_bar! Look at the code!

ggplot(piechart_df, aes("", Proportion, fill = Type)) +
    geom_bar(width = 1, size = 1, color = "white", 
          stat = "identity") +
    coord_polar("y") +
    geom_text(aes(label = paste0(round(Proportion*100,0), "%")), 
              position = position_stack(vjust = 0.5)) +
    labs(x = NULL, y = NULL, fill = NULL, 
         title = "Distribution of Media Conditions Tested") +
    guides(fill = guide_legend(reverse = TRUE)) +
    scale_fill_manual(values = pie_colors) +
    theme_classic() +
    theme(axis.line = element_blank(),
          axis.text = element_blank(),
          axis.ticks = element_blank(),
          plot.title = element_text(hjust = 0.5, 
            color = "saddlebrown"))

So, let’s talk about this code! How do we get geom_bar to be a pie chart? This is how:

  • On the aes line to launch the chart, notice how the x value is set at “”. That’s because it doesn’t matter. It’s a pie chart, so it doesn’t have an x – only a y.
  • The circular style is achieved with geom_bar + coord_polar. The geom_bar line describes a white, unshapen bar, and coord_polar(“y”) is what turns it into a circle.
  • The geom_text line turns the proportions into percent, and adds them as data labels. Notice the position option to move the label a little so it’s not so crowded.
  • labs fills in the labels I want to fill in.
  • guides format the legend. For whatever reason, I wanted the legend listed in reverse of the default, which explains the reverse = TRUE option.
  • Scale_fill_manual tells ggplot2 to use the color vector for the colors we specified and overwrite the default colors.
  • Theme commands after that include theme_classic() (to give it a clean, uncluttered theme), and the theme command to format the plot title with a particular color, and to suppress a lot of elements that look ugly in default on a pie chart.

Updated April 20, 2022. Photograph of pies by Haem85, available here.

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Pie chart ggplot style is surprisingly hard to make, mainly because ggplot2 did not give us a circle shape to deal with. But I explain how to get around it in my blog pot.

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