Many years ago I was asked to demo a new ggplot2 extension. It was supposed to be a paid project, but it didn’t work out. I had the demo half done, and as i moved to work on other things – including not making plots regularly as part of my work – I forgot about it.
Then as I was doing maintenance of some other R packages, I noticed the folder on my computer. Fast-forward to now, and the v0.1.0 of this package is on it’s way to CRAN.
{ggindex} is a new ggplot2 extension that marks points with numbers and explains the numbers in a legend, the way a campus map lists buildings beside the plan.
That layout is common on maps and in annotated figures, but ggplot2 has no direct way to draw it – at least that I know of. Usually, a legend key shows a symbol: a coloured dot, a line, a square. It cannot show the number written next to a point, so the reader has to match labels to descriptions by eye.
Meet geom_focus()
Map info to the description that belongs in the legend, and geom_focus() does the rest: it numbers the points 1, 2, 3 in data order, draws each number in a marker, and builds a legend whose keys carry the same numbers.
# install.packages("pak")
pak::pak("discindo/ggindex")
library(ggplot2)
library(ggindex)
sites <- data.frame(
x = c(6, 7, 8, 9, 10),
y = c(6, 9, 7, 10, 8),
name = c("Library", "Main hall", "Sports centre", "Cafeteria", "Car park")
)
ggplot(sites, aes(x, y, info = name)) +
geom_focus() +
theme_minimal()To choose the numbers yourself, for example a rank or a building code, map label as well. The legend is then sorted by label, so it reads in the same order as the numbers.
Focus on a few points
Usually only a handful of points deserve a number. Map focus to a logical variable and only those observations get a marker; add geom_point() underneath to show the rest.
cars <- mtcars
cars$model <- rownames(cars)
cars$rank <- rank(-cars$mpg, ties.method = "first")
ggplot(cars, aes(wt, mpg)) +
geom_point(colour = "grey60") +
geom_focus(aes(label = rank, focus = rank <= 5, info = model)) +
scale_info_discrete("Most efficient") +
labs(x = "Weight (1000 lbs)", y = "Miles per gallon")See more on the package’s website: discindo.github.io/ggindex/