Skip to contents

Ridge Plot (Stacked Density Plot)

Source: R/plotRidge.R
plotRidge.Rd

Draws stacked kernel density estimates (ridge plot) for grouped data. Each group is displayed as a density curve shifted along the y-axis.

Usage

# Default S3 method
plotRidge(
  x,
  ...,
  main = NULL,
  xlab = "",
  ylab = "",
  xlim = NULL,
  ylim = NULL,
  bw = "nrd0",
  normalize = c("global", "group"),
  add = FALSE,
  scale = 1,
  spacing = 1,
  col = NULL,
  border = NULL,
  lwd = 1,
  lty = 1,
  fill = TRUE,
  grid = NA,
  stamp = .useTheme
)

# S3 method for class 'formula'
plotRidge(
  formula,
  data,
  subset,
  na.action = na.omit,
  main = NULL,
  xlab = "",
  ylab = "",
  ...
)

Arguments

x

a numeric vector, or a list of numeric vectors representing groups.

...

further numeric vectors (unnamed), each forming a group, or graphical parameters passed to par().

main

main title. NULL (default) draws none, unless the theme sets autoTitle = TRUE (see theme); the title is then derived from the input: the names of the data arguments, or the formula. "", NA or FALSE always suppress it and compact the top margin; any other string is used as given.

xlab, ylab

axis labels. For the formula method, empty labels default to the response and the grouping variable.

xlim, ylim

axis limits.

bw

bandwidth for stats::density().

normalize

how the density heights are scaled to scale: "global" (default) divides all densities by the highest peak of all groups, so that heights stay comparable across groups (as in ggridges); "group" divides each density by its own peak, so that every ridge reaches the full height. Use the latter when a single narrow group would otherwise flatten all others.

add

logical; if TRUE, adds to an existing plot.

scale

scaling factor for density height.

spacing

vertical spacing between ridges.

col

fill color(s), recycled over the groups. NULL (default) uses the palette.

border

border color(s), recycled over the groups. NULL (default) uses col.

lwd

line width(s).

lty

line type(s).

fill

logical; fill area under densities.

grid

logical, NA, or list controlling grid.

stamp

controls the corner stamp. .useTheme (default) resolves to getTheme()$stamp. TRUE/FALSE/NULL, a string, or a named list for stamp().

formula

a formula of the form y ~ group, or y ~ a:b for the cells of several grouping variables. y ~ a + b is not accepted, see bedrock::resolveFormula().

data

an optional data frame containing the variables in the formula.

subset

an optional expression indicating which observations to use, evaluated in data (subset = len > 10), as in boxplot().

na.action

a function specifying how missing values are handled, defaults to na.omit().

Value

Invisibly returns NULL.

Details

Ridge plots are useful for comparing distributions across multiple groups. Each density is normalized and vertically offset, improving readability compared to overlaid density plots.

See also

plotDens()

Examples

set.seed(1)
df <- data.frame(
  value = c(rnorm(100), rnorm(100, 2), rnorm(100, 4)),
  group = rep(c("A", "B", "C"), each = 100)
)

plotRidge(value ~ group, data = df)


# subset and the cells of two grouping variables
plotRidge(len ~ supp:dose, ToothGrowth, subset = len > 8)


# the narrow group VC:0.5 flattens all others; scale each ridge to its
# own peak instead
plotRidge(len ~ supp:dose, ToothGrowth, subset = len > 8,
          normalize = "group")