ggplot: Easy as pie (charts)

_{This post by no means endorses the use of pie charts. But, if you must, here’s how…}

For some reason, the top Google results for “ggplot2 pie chart” show some very convoluted code to accomplish what should be easy:

1. Make slices
2. Add labels to the middle of those slices

Instead, let’s look at the easy way - with position_stack()!

Make some data

We first need some data fit for a pie chart - a column for slice label, and a column for their (preferably relative) size.

d <- data.frame(
  Slices = c("Writing code", "Staring at plot", "Fixing code", "Enjoying plot") |> rep(2),
  Time = c(1, 5, 4, 2, 1, 1, 1, 2),
  When = c("Before reading this post", "After reading this post") |> rep(each = 4)
) |>
  transform(
    # Make time relative
    Time_relative = Time / ave(Time, When, FUN = sum),
    Slices = factor(Slices, levels = unique(Slices)),
    When = factor(When, levels = unique(When))
  )

d

#>            Slices Time                     When Time_relative
#> 1    Writing code    1 Before reading this post    0.08333333
#> 2 Staring at plot    5 Before reading this post    0.41666667
#> 3     Fixing code    4 Before reading this post    0.33333333
#> 4   Enjoying plot    2 Before reading this post    0.16666667
#> 5    Writing code    1  After reading this post    0.20000000
#> 6 Staring at plot    1  After reading this post    0.20000000
#> 7     Fixing code    1  After reading this post    0.20000000
#> 8   Enjoying plot    2  After reading this post    0.40000000

Now let’s build the pie-chart!

library(ggplot2)

ggplot(d, aes(x = 1, y = Time_relative, fill = Slices)) +
  facet_grid(cols = vars(When)) + 
  # Make pie
  coord_polar(theta = "y") +
  # Add the *stacked* columns
  geom_col(position = position_stack(reverse = TRUE), 
           color = "tan3", linewidth = 3, show.legend = FALSE) + 
  # Add labels to the *stacked* position,
  # in the middle of the column (vjust = 0.5)
  geom_text(aes(label = Slices), 
            position = position_stack(vjust = 0.5, reverse = TRUE)) + 
  # Make it a pizza pie!
  see::scale_fill_pizza_d() + 
  theme_void() + 
  labs(title = "Relative time spent building piecharts with ggplot2")

Best served HOT!