Plot ridgelines and ridgeline plots with fill gradients along the x axis

The geoms geom_ridgeline_gradient and geom_density_ridges_gradient work just like geom_ridgeline and geom_density_ridges except that the fill aesthetic can vary along the x axis. Because filling with color gradients is fraught with issues, these geoms should be considered experimental. Don't use them unless you really need to. Note that due to limitations in R's graphics system, transparency (alpha) has to be disabled for gradient fills.

geom_ridgeline_gradient(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  na.rm = FALSE,
  gradient_lwd = 0.5,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

geom_density_ridges_gradient(
  mapping = NULL,
  data = NULL,
  stat = "density_ridges",
  position = "points_sina",
  panel_scaling = TRUE,
  na.rm = TRUE,
  gradient_lwd = 0.5,
  show.legend = NA,
  inherit.aes = TRUE,
  ...
)

Arguments

mapping	Set of aesthetic mappings created by `aes()` or `aes_()`. If specified and `inherit.aes = TRUE` (the default), it is combined with the default mapping at the top level of the plot. You must supply `mapping` if there is no plot mapping.
data	The data to be displayed in this layer. There are three options: If `NULL`, the default, the data is inherited from the plot data as specified in the call to `ggplot()`. A `data.frame`, or other object, will override the plot data. A `function` will be called with a single argument, the plot data. The return value must be a `data.frame.`, and will be used as the layer data.
stat	The statistical transformation to use on the data for this layer, as a string.
position	Position adjustment, either as a string, or the result of a call to a position adjustment function.
na.rm	If `FALSE`, the default, missing values are removed with a warning. If `TRUE`, missing values are silently removed.
gradient_lwd	A parameter to needed to remove rendering artifacts inside the rendered gradients. Should ideally be 0, but often needs to be around 0.5 or higher.
show.legend	logical. Should this layer be included in the legends? `NA`, the default, includes if any aesthetics are mapped. `FALSE` never includes, and `TRUE` always includes.
inherit.aes	If `FALSE`, overrides the default aesthetics, rather than combining with them.
...	other arguments passed on to `layer()`. These are often aesthetics, used to set an aesthetic to a fixed value, like `color = "red"` or `size = 3`. They may also be parameters to the paired geom/stat.
panel_scaling	Argument only to `geom_density_ridges_gradient`. If `TRUE`, the default, relative scaling is calculated separately for each panel. If `FALSE`, relative scaling is calculated globally.

Examples

library(ggplot2)

# Example for `geom_ridgeline_gradient()`
d <- data.frame(
  x = rep(1:5, 3) + c(rep(0, 5), rep(0.3, 5), rep(0.6, 5)),
  y = c(rep(0, 5), rep(1, 5), rep(3, 5)),
  height = c(0, 1, 3, 4, 0, 1, 2, 3, 5, 4, 0, 5, 4, 4, 1)
)
ggplot(d, aes(x, y, height = height, group = y, fill = factor(x+y))) +
  geom_ridgeline_gradient() +
  scale_fill_viridis_d(direction = -1) +
  theme(legend.position = 'none')

# Example for `geom_density_ridges_gradient()`
ggplot(lincoln_weather, aes(x = `Mean Temperature [F]`, y = `Month`, fill = stat(x))) +
  geom_density_ridges_gradient(scale = 3, rel_min_height = 0.01) +
  scale_x_continuous(expand = c(0, 0)) +
  scale_y_discrete(expand = c(0, 0)) +
  scale_fill_viridis_c(name = "Temp. [F]", option = "C") +
  coord_cartesian(clip = "off") +
  labs(title = 'Temperatures in Lincoln NE in 2016') +
  theme_ridges(font_size = 13, grid = TRUE) +
  theme(axis.title.y = element_blank())
#> Picking joint bandwidth of 3.37