In wilkox/treemapify: Draw Treemaps in 'ggplot2'

library(knitr)
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  fig.path = "man/figures/README-"
)

treemapify

treemapify provides ggplot2 geoms for drawing treemaps.

Installation

Install the release version of treemapify from CRAN:

install.packages("treemapify")

If you want the development version, install it from GitHub:

devtools::install_github("wilkox/treemapify")

The G20 dataset

treemapify includes an example dataset containing statistics about the G-20 group of major world economies.

library(ggplot2)
library(treemapify)
G20

Drawing a simple treemap

In a treemap, each tile represents a single observation, with the area of the tile proportional to a variable. Let's start by drawing a treemap with each tile representing a G-20 country. The area of the tile will be mapped to the country's GDP, and the tile's fill colour mapped to its HDI (Human Development Index). geom_treemap() is the basic geom for this purpose.

ggplot(G20, aes(area = gdp_mil_usd, fill = hdi)) +
  geom_treemap()

This plot isn't very useful without the knowing what country is represented by each tile. geom_treemap_text() can be used to add a text label to each tile. It uses the ggfittext package to resize the text so it fits the tile. In addition to standard text formatting aesthetics you would use in geom_text(), like fontface or colour, we can pass additional options specific for ggfittext. For example, we can place the text in the centre of the tile with place = "centre", and expand it to fill as much of the tile as possible with grow = TRUE.

ggplot(G20, aes(area = gdp_mil_usd, fill = hdi, label = country)) +
  geom_treemap() +
  geom_treemap_text(fontface = "italic", colour = "white", place = "centre",
                    grow = TRUE)

Subgrouping tiles

geom_treemap() supports subgrouping of tiles within a treemap by passing a subgroup aesthetic. Let's subgroup the countries by region, draw a border around each subgroup with geom_treemap_subgroup_border(), and label each subgroup with geom_treemap_subgroup_text(). geom_treemap_subgroup_text() takes the same arguments for text placement and resizing as geom_treemap_text().

ggplot(G20, aes(area = gdp_mil_usd, fill = hdi, label = country,
                subgroup = region)) +
  geom_treemap() +
  geom_treemap_subgroup_border() +
  geom_treemap_subgroup_text(place = "centre", grow = T, alpha = 0.5, colour =
                             "black", fontface = "italic", min.size = 0) +
  geom_treemap_text(colour = "white", place = "topleft", reflow = T)

Note that Argentina is not labelled. geom_treemap_text() will hide text labels that cannot fit a tile without being shrunk below a minimum size, by default 4 points. This can be adjusted with the min.size argument.

Up to three nested levels of subgrouping are supported with the subgroup2 and subgroup3 aesthetics. Borders and text labels for these subgroups can be drawn with geom_treemap_subgroup2_border(), etc. Note that ggplot2 draws plot layers in the order that they are added. This means it is possible to accidentally hide one layer of subgroup borders with another. Usually, it's best to add the border layers in order from deepest to shallowest, i.e. geom_treemap_subgroup3_border() then geom_treemap_subgroup2_border() then geom_treemap_subgroup_border().

ggplot(G20, aes(area = 1, label = country, subgroup = hemisphere,
                subgroup2 = region, subgroup3 = econ_classification)) +
  geom_treemap() +
  geom_treemap_subgroup3_border(colour = "blue", size = 1) +
  geom_treemap_subgroup2_border(colour = "white", size = 3) +
  geom_treemap_subgroup_border(colour = "red", size = 5) +
  geom_treemap_subgroup_text(place = "middle", colour = "red", alpha = 0.5, grow = T) +
  geom_treemap_subgroup2_text(colour = "white", alpha = 0.5, fontface = "italic") +
  geom_treemap_subgroup3_text(place = "top", colour = "blue", alpha = 0.5) +
  geom_treemap_text(colour = "white", place = "middle", reflow = T)

As demonstrated, there is no assurance that the resulting plot will look good.

Like any ggplot2 plot, treemapify plots can be faceted, scaled, themed, etc.

ggplot(G20, aes(area = gdp_mil_usd, fill = region, label = country, subgroup = region)) +
  geom_treemap() +
  geom_treemap_text(grow = T, reflow = T, colour = "black") +
  facet_wrap( ~ hemisphere) +
  scale_fill_brewer(palette = "Set1") +
  theme(legend.position = "bottom") +
  labs(
    title = "The G-20 major economies by hemisphere",
    caption = "The area of each tile represents the country's GDP as a
      proportion of all countries in that hemisphere",
    fill = "Region"
  )

Animated treemaps

The default algorithm for laying out the tiles is the 'squarified' algorithm. This tries to minimise the tiles' aspect ratios, making sure there are no long and flat or tall and skinny tiles. While 'squarified' treemaps are aesthetically pleasing, the downside is that the position of tiles within the plot area can change dramatically with even small changes to the dataset. This makes it difficult to compare treemaps side-by-side, or create animated treemaps.

By providing the layout = "fixed" option to treemapify geoms, an alternative layout algorithm is used that will always position the tiles based on the order of observations in the data frame. It's very important that the same value for layout is passed to all treemapify geoms, otherwise different layers of the plot might not share the same layout.

With the help of layout = "fixed", and with the gganimate package, it becomes possible to create animated treemaps showing e.g. change over time.

library(gganimate)
library(gapminder)

p <- ggplot(gapminder, aes(
    label = country,
    area = pop,
    subgroup = continent,
    fill = lifeExp
  )) +
  geom_treemap(layout = "fixed") +
  geom_treemap_text(layout = "fixed", place = "centre", grow = TRUE, colour = "white") +
  geom_treemap_subgroup_text(layout = "fixed", place = "centre") +
  geom_treemap_subgroup_border(layout = "fixed") +
  transition_time(year) +
  ease_aes('linear') +
  labs(title = "Year: {frame_time}")

anim_save("man/figures/animated_treemap.gif", p, nframes = 48)