Ridge Plot — RidgePlot • plotthis

Ridge (joy) plot for visualising the distribution of a numeric variable across multiple groups. Each group is rendered as a partially overlapping density curve along the y-axis, making it easy to compare distribution shapes, central tendency, and spread across categories.

The function supports both long and wide data formats:

Long form (in_form = "long", default) — a numeric column (x) plus a factor column (group_by) whose levels become the y-axis ridges.
Wide form (in_form = "wide") — multiple numeric columns listed in group_by are gathered internally into long form.

Optional vertical reference lines (add_vline) can mark group means, specific values, or per-group thresholds. Supports faceting, split-by splitting, and full palette customisation.

Usage

RidgePlot(
  data,
  x = NULL,
  in_form = c("long", "wide"),
  split_by = NULL,
  split_by_sep = "_",
  group_by = NULL,
  group_by_sep = "_",
  group_name = NULL,
  scale = NULL,
  keep_na = FALSE,
  keep_empty = FALSE,
  add_vline = NULL,
  vline_type = "solid",
  vline_color = TRUE,
  vline_width = 0.5,
  vline_alpha = 1,
  flip = FALSE,
  alpha = 0.8,
  theme = "theme_this",
  theme_args = list(),
  palette = "Paired",
  palcolor = NULL,
  palreverse = FALSE,
  title = NULL,
  subtitle = NULL,
  xlab = NULL,
  ylab = NULL,
  x_text_angle = 90,
  reverse = FALSE,
  facet_by = NULL,
  facet_scales = "fixed",
  facet_ncol = NULL,
  facet_nrow = NULL,
  facet_byrow = TRUE,
  aspect.ratio = 1,
  legend.position = "none",
  legend.direction = "vertical",
  combine = TRUE,
  nrow = NULL,
  ncol = NULL,
  byrow = TRUE,
  seed = 8525,
  axes = NULL,
  axis_titles = axes,
  guides = NULL,
  design = NULL,
  ...
)

Arguments

data

A data frame.

x

A character string specifying the column name of the data frame to plot for the x-axis.

in_form

A character string specifying whether data is in "long" (default) or "wide" format.

split_by

The column(s) to split data by and plot separately.

split_by_sep

The separator for multiple split_by columns. See split_by

group_by

Columns to group the data for plotting For those plotting functions that do not support multiple groups, They will be concatenated into one column, using group_by_sep as the separator

group_by_sep

The separator for multiple group_by columns. See group_by

group_name

A character string used as the legend title for the group_by fill aesthetic. Defaults to the (concatenated) group_by column name.

scale

A numeric value controlling the vertical overlap of ridges. Passed to ggridges::geom_density_ridges(scale = ...). Smaller values increase overlap. When NULL, ggridges auto-computes the scale.

keep_na

A logical value or a character to replace the NA values in the data. It can also take a named list to specify different behavior for different columns. If TRUE or NA, NA values will be replaced with NA. If FALSE, NA values will be removed from the data before plotting. If a character string is provided, NA values will be replaced with the provided string. If a named vector/list is provided, the names should be the column names to apply the behavior to, and the values should be one of TRUE, FALSE, or a character string. Without a named vector/list, the behavior applies to categorical/character columns used on the plot, for example, the x, group_by, fill_by, etc.

keep_empty

One of FALSE, TRUE and "level". It can also take a named list to specify different behavior for different columns. Without a named list, the behavior applies to the categorical/character columns used on the plot, for example, the x, group_by, fill_by, etc.

FALSE (default): Drop empty factor levels from the data before plotting.
TRUE: Keep empty factor levels and show them as a separate category in the plot.
"level": Keep empty factor levels, but do not show them in the plot. But they will be assigned colors from the palette to maintain consistency across multiple plots. Alias: levels

add_vline

A specification for vertical reference lines:

NULL or FALSE: no lines.
TRUE: draw a line at the mean of each group.
A numeric vector: draw the same lines for all groups.
A named list of numeric vectors: per-group lines, where names should match group_by levels.

vline_type

A character string specifying the line type for the vertical reference lines. Passed as linetype to geom_vline(). Default: "solid".

vline_color

The colour of the vertical reference lines:

A literal colour value or vector (recycled): applied directly.
TRUE (default): each line is coloured with a darkened blend of the corresponding ridge fill colour, computed via blend_colors(mode = "multiply").

vline_width

A numeric value for the thickness of the vertical reference lines. Passed as linewidth to geom_vline(). Default: 0.5.

vline_alpha

A numeric value in [0, 1] for the transparency of the vertical reference lines. Default: 1.

flip

A logical value. If TRUE, the axes are swapped via coord_flip(). X-axis text angle and grid-line placement are adjusted accordingly.

alpha

A numeric value specifying the transparency of the plot.

theme

A character string or a theme class (i.e. ggplot2::theme_classic) specifying the theme to use. Default is "theme_this".

theme_args

A list of arguments to pass to the theme function.

palette

A character string specifying the palette to use. A named list or vector can be used to specify the palettes for different split_by values.

palcolor

A character string specifying the color to use in the palette. A named list can be used to specify the colors for different split_by values. If some values are missing, the values from the palette will be used (palcolor will be NULL for those values).

palreverse

A logical value indicating whether to reverse the palette. Default is FALSE.

title

A character string specifying the title of the plot. A function can be used to generate the title based on the default title. This is useful when split_by is used and the title needs to be dynamic.

subtitle

A character string specifying the subtitle of the plot.

xlab

A character string specifying the x-axis label.

ylab

A character string specifying the y-axis label.

x_text_angle

A numeric value specifying the angle of the x-axis text.

reverse

A logical value. If TRUE, the y-axis group order is reversed. NA groups are renamed to the literal string "NA" and placed at the end.

facet_by

A character string specifying the column name of the data frame to facet the plot. Otherwise, the data will be split by split_by and generate multiple plots and combine them into one using patchwork::wrap_plots

facet_scales

Whether to scale the axes of facets. Default is "fixed" Other options are "free", "free_x", "free_y". See ggplot2::facet_wrap

facet_ncol

A numeric value specifying the number of columns in the facet. When facet_by is a single column and facet_wrap is used.

facet_nrow

A numeric value specifying the number of rows in the facet. When facet_by is a single column and facet_wrap is used.

facet_byrow

A logical value indicating whether to fill the plots by row. Default is TRUE.

aspect.ratio

A numeric value specifying the aspect ratio of the plot.

legend.position

A character string specifying the position of the legend. if waiver(), for single groups, the legend will be "none", otherwise "right".

legend.direction

A character string specifying the direction of the legend.

combine

Whether to combine the plots into one when facet is FALSE. Default is TRUE.

nrow

A numeric value specifying the number of rows in the facet.

ncol

A numeric value specifying the number of columns in the facet.

byrow

A logical value indicating whether to fill the plots by row.

seed

The random seed to use. Default is 8525.

axes

A string specifying how axes should be treated. Passed to patchwork::wrap_plots(). Only relevant when split_by is used and combine is TRUE. Options are:

'keep' will retain all axes in individual plots.
'collect' will remove duplicated axes when placed in the same run of rows or columns of the layout.
'collect_x' and 'collect_y' will remove duplicated x-axes in the columns or duplicated y-axes in the rows respectively.

axis_titles

A string specifying how axis titltes should be treated. Passed to patchwork::wrap_plots(). Only relevant when split_by is used and combine is TRUE. Options are:

'keep' will retain all axis titles in individual plots.
'collect' will remove duplicated titles in one direction and merge titles in the opposite direction.
'collect_x' and 'collect_y' control this for x-axis titles and y-axis titles respectively.

guides

A string specifying how guides should be treated in the layout. Passed to patchwork::wrap_plots(). Only relevant when split_by is used and combine is TRUE. Options are:

'collect' will collect guides below to the given nesting level, removing duplicates.
'keep' will stop collection at this level and let guides be placed alongside their plot.
'auto' will allow guides to be collected if a upper level tries, but place them alongside the plot if not.

design

Specification of the location of areas in the layout, passed to patchwork::wrap_plots(). Only relevant when split_by is used and combine is TRUE. When specified, nrow, ncol, and byrow are ignored. See patchwork::wrap_plots() for more details.

...

Additional arguments.

Value

A ggplot object (single plot), a patchwork / wrap_plots object (when split_by is provided and combine = TRUE), or a list of ggplot objects (when split_by is provided and combine = FALSE).

split_by Workflow

When split_by is specified, RidgePlot() executes the following pipeline:

Argument validation — validate_common_args() checks the seed and facet-by consistency.
NA / empty normalisation — check_keep_na() / check_keep_empty() convert keep_na / keep_empty to per-column lists.
Theme resolution — process_theme() resolves the theme string to a theme function.
Split column resolution — check_columns() validates split_by (force_factor, concat_multi).
Pre-filtering — process_keep_na_empty() removes NA / empty levels from the split column, then data is split by split_by levels (order preserved).
Per-split parameter resolution — check_palette(), check_palcolor(), check_legend() resolve palette, palcolor, legend.position, and legend.direction for each split.
Per-split dispatch — each split is passed to RidgePlotAtomic() with its resolved parameters. Title defaults to the split level name unless title is a function (in which case it is called with the default).
Combination — combine_plots() assembles the list of plots via patchwork::wrap_plots(), applying nrow, ncol, byrow, axes, axis_titles, guides, and design.

Examples

# \donttest{
set.seed(8525)
data <- data.frame(
   x = c(rnorm(250, -1), rnorm(250, 1)),
   group = factor(rep(c("A", NA, LETTERS[3:5]), each = 100), levels = LETTERS[1:6])
)

# basic usage
RidgePlot(data, x = "x")  # single ridge (no group_by)
#> Picking joint bandwidth of 0.371

RidgePlot(data, x = "x", add_vline = 0, vline_color = "black")
#> Picking joint bandwidth of 0.371


# grouped ridges
RidgePlot(data, x = "x", group_by = "group")
#> Picking joint bandwidth of 0.385

RidgePlot(data, x = "x", group_by = "group",
   keep_na = TRUE, keep_empty = TRUE)
#> Picking joint bandwidth of 0.378

RidgePlot(data, x = "x", group_by = "group", reverse = TRUE)
#> Picking joint bandwidth of 0.385

RidgePlot(data, x = "x", group_by = "group",
   add_vline = TRUE, vline_color = TRUE, alpha = 0.7)
#> Picking joint bandwidth of 0.385


# faceting
RidgePlot(data, x = "x", facet_by = "group",
   keep_na = TRUE, keep_empty = TRUE)
#> Picking joint bandwidth of 0.356
#> Picking joint bandwidth of NaN
#> Warning: no non-missing arguments to min; returning Inf
#> Warning: no non-missing arguments to max; returning -Inf
#> Picking joint bandwidth of 0.518
#> Picking joint bandwidth of 0.361
#> Picking joint bandwidth of 0.307
#> Picking joint bandwidth of NaN
#> Warning: no non-missing arguments to min; returning Inf
#> Warning: no non-missing arguments to max; returning -Inf
#> Picking joint bandwidth of 0.347
#> Picking joint bandwidth of 0.356
#> Picking joint bandwidth of NaN
#> Warning: no non-missing arguments to min; returning Inf
#> Warning: no non-missing arguments to max; returning -Inf
#> Picking joint bandwidth of 0.518
#> Picking joint bandwidth of 0.361
#> Picking joint bandwidth of 0.307
#> Picking joint bandwidth of NaN
#> Warning: no non-missing arguments to min; returning Inf
#> Warning: no non-missing arguments to max; returning -Inf
#> Picking joint bandwidth of 0.347


# wide form
data_wide <- data.frame(
   A = rnorm(100),
   B = rnorm(100),
   C = rnorm(100),
   D = rnorm(100),
   E = rnorm(100),
   group = sample(letters[1:4], 100, replace = TRUE)
)
RidgePlot(data_wide, group_by = LETTERS[1:5], in_form = "wide")
#> Warning: Column 'A' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_empty' processing for this column.
#> Picking joint bandwidth of 0.337

RidgePlot(data_wide, group_by = LETTERS[1:5], in_form = "wide", facet_by = "group")
#> Warning: Column 'A' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_empty' processing for this column.
#> Picking joint bandwidth of 0.429
#> Picking joint bandwidth of 0.416
#> Picking joint bandwidth of 0.367
#> Picking joint bandwidth of 0.428
#> Picking joint bandwidth of 0.429
#> Picking joint bandwidth of 0.416
#> Picking joint bandwidth of 0.367
#> Picking joint bandwidth of 0.428


# split_by with per-split palettes
RidgePlot(data_wide, group_by = LETTERS[1:5], in_form = "wide", split_by = "group",
   palette = list(a = "Reds", b = "Blues", c = "Greens", d = "Purples"))
#> Warning: Column 'A' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_na' processing for this column.
#> Warning: Column 'A' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'B' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'C' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'D' not found in data. Skipping 'keep_empty' processing for this column.
#> Warning: Column 'E' not found in data. Skipping 'keep_empty' processing for this column.
#> Picking joint bandwidth of 0.429
#> Picking joint bandwidth of 0.416
#> Picking joint bandwidth of 0.367
#> Picking joint bandwidth of 0.428

# }