classbound_palette: Generate deterministic colors for classification classes

In classbound: Visualization for Classification Decision Boundaries

Generate deterministic colors for classification classes

Description

Returns a named character vector mapping class labels to hex color codes. Colors are assigned deterministically: class labels are sorted alphabetically before assignment, so the same class always receives the same color regardless of the order the classes are supplied.

Usage

classbound_palette(classes)

Arguments

classes

A character vector or factor containing class labels. Duplicates and NA values are handled gracefully.

Details

The first 20 classes are assigned colors from a curated palette of visually distinct hues designed for use on both light and dark backgrounds. For more than 20 classes, additional colors are generated using the golden-angle method (hue = (index * phi) %% 1 where ⁠phi = 0.618...⁠), which produces perceptually distinct colors with uniform spacing in HCL space.

plot_boundary() uses this palette by default. If an RColorBrewer palette is requested via ⁠palette =⁠ but cannot accommodate the number of classes (e.g., "Dark2" supports a maximum of 8), it automatically falls back to classbound_palette().

Value

A named character vector where names are the unique sorted class labels and values are hex color codes (e.g., "#E6194B").

See Also

plot_boundary()

Examples

# 3-class palette
classbound_palette(c("Adelie", "Chinstrap", "Gentoo"))

# Colors are alphabetically ordered, so order of input doesn't matter
identical(
  classbound_palette(c("B", "A", "C")),
  classbound_palette(c("C", "A", "B"))
)

# Use in plot_boundary() via the palette argument

library(palmerpenguins)
data(penguins)
peng_data <- na.omit(penguins[, c("species", "bill_length_mm", "bill_depth_mm")])
m <- fit_model(peng_data, species ~ ., rpart::rpart)
m <- boundary_compute(m, resolution = 50)
plot_boundary(m,
  obs_data = peng_data, x_col = "bill_length_mm",
  y_col = "bill_depth_mm", true_label = "species"
)

classbound documentation built on Sept. 30, 2026, 5:13 p.m.