gg_hdrboxplot: HDR plot

In weird: Functions and Data Sets for "That's Weird: Anomaly Detection Using R" by Rob J Hyndman

HDR plot

Description

Produces a 1d or 2d box plot of HDR regions. The darker regions contain observations with higher probability, while the lighter regions contain points with lower probability. Observations outside the largest HDR are shown as individual points. Anomalies with leave-one-out surprisal probabilities less than 0.005 are optionally shown in black.

Usage

gg_hdrboxplot(
  data,
  var1,
  var2 = NULL,
  prob = c(0.5, 0.99),
  color = "#0072b2",
  show_points = FALSE,
  show_anomalies = TRUE,
  alpha = NULL,
  jitter = TRUE,
  ngrid = 501,
  ...
)

Arguments

data	A data frame or matrix containing the data.
var1	The name of the first variable to plot (a bare expression).
var2	Optionally, the name of the second variable to plot (a bare expression).
prob	A numeric vector specifying the coverage probabilities for the HDRs.
color	The base color to use for the mode. Colors for the HDRs are generated by whitening this color.
show_points	A logical argument indicating if a regular HDR plot is required (FALSE), or whether to show the individual observations in the same colors (TRUE).
show_anomalies	A logical argument indicating if the surprisal anomalies should be shown (in black). These are points with leave-one-out surprisal probability values less than 0.005 (using a GPD approximation), and which lie outside the 99% HDR region.
alpha	Transparency of points. Ignored if show_points is FALSE. Defaults to min(1, 500/n), where n is the number of observations plotted.
jitter	A logical value indicating if the points should be vertically jittered for the 1d box plots to reduce overplotting.
ngrid	Number of grid points to use for the density function.
...	Other arguments passed to dist_kde.

Details

The original HDR boxplot proposed by Hyndman (1996), can be produced with show_anomalies = FALSE, jitter = FALSE, alpha = 1, and all other arguments set to their defaults.

Value

A ggplot object showing an HDR plot or scatterplot of the data.

Author(s)

Rob J Hyndman

References

Hyndman, R J (1996) Computing and Graphing Highest Density Regions, The American Statistician, 50(2), 120–126. https://robjhyndman.com/publications/hdr/

Rob J Hyndman (2026) "That's weird: Anomaly detection using R", Section 5.7, https://OTexts.com/weird/.

See Also

surprisals, hdr_table

Examples

df <- data.frame(x = c(rnorm(1000), rnorm(1000, 5, 1), 10))
gg_hdrboxplot(df, x, show_anomalies = TRUE)
cricket_batting |>
  filter(Innings > 20) |>
  gg_hdrboxplot(Average)
oldfaithful |>
  gg_hdrboxplot(duration, waiting, show_points = TRUE)

weird documentation built on Jan. 27, 2026, 9:06 a.m.