TrendPlot: Trend plot

In plotthis: High-Level Plotting Built Upon 'ggplot2' and Other Plotting Packages

Trend plot

Description

Draws a trend plot combining stacked bars with a semi-transparent area background to show how one or more groups accumulate across a discrete x-axis variable. This hybrid style sits between a bar plot and an area plot: it preserves the discrete category separation of bars while softening the visual with an area fill, making trends across categories easier to perceive.

The function supports count aggregation (omit y to plot observation counts per x-category), proportion scaling (scale_y = TRUE normalises each x position to 100\ colour control, faceting, and splitting into separate sub-plots via split_by.

Usage

TrendPlot(
  data,
  x,
  y = NULL,
  x_sep = "_",
  split_by = NULL,
  split_by_sep = "_",
  group_by = NULL,
  group_by_sep = "_",
  group_name = NULL,
  scale_y = FALSE,
  theme = "theme_this",
  theme_args = list(),
  palette = "Paired",
  palcolor = NULL,
  palreverse = FALSE,
  alpha = 1,
  facet_by = NULL,
  facet_scales = "fixed",
  facet_ncol = NULL,
  facet_nrow = NULL,
  facet_byrow = TRUE,
  x_text_angle = 0,
  aspect.ratio = 1,
  legend.position = waiver(),
  legend.direction = "vertical",
  title = NULL,
  subtitle = NULL,
  xlab = NULL,
  ylab = NULL,
  keep_na = FALSE,
  keep_empty = FALSE,
  seed = 8525,
  combine = TRUE,
  nrow = NULL,
  ncol = NULL,
  byrow = TRUE,
  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.
y	A character string specifying the column name of the data frame to plot for the y-axis.
x_sep	A character string used to join multiple x columns. Default "_". Ignored when x is a single column.
split_by	The column(s) to split the data by and produce separate sub-plots. Multiple columns are concatenated with split_by_sep.
split_by_sep	A character string to separate concatenated split_by columns. Default "_".
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 fill legend title. When NULL, the group_by column name is used.
scale_y	A logical value. When TRUE, y-values are scaled to proportions within each (x, facet_by) group so that each x position stacks to 1.0. The y-axis labels switch from numeric to percent format automatically.
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.
alpha	A numeric value specifying the transparency of the plot.
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.
x_text_angle	A numeric value specifying the angle of the x-axis text.
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.
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.
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
seed	A numeric seed for reproducibility. Passed to validate_common_args().
combine	Logical; when TRUE (default), returns a combined patchwork object. When FALSE, returns a named list of individual ggplot objects.
ncol, nrow	Integer number of columns / rows for the combined layout (passed to wrap_plots).
byrow	Logical; fill the combined layout by row. Default TRUE (passed to wrap_plots).
axes	A character string specifying how axes should be treated across the combined layout (passed to wrap_plots).
axis_titles	A character string specifying how axis titles should be treated across the combined layout. Defaults to axes.
guides	A character string specifying how guides (legends) should be collected across panels. Default "collect" (passed to combine_plots()).
design	A custom layout design for the combined plot (passed to combine_plots()).
...	Additional arguments.

Value

A ggplot object, a patchwork object, or a named list of ggplot objects (when combine = FALSE), each with height and width attributes in inches.

split_by workflow

When split_by is provided:

1. check_keep_na() and check_keep_empty() normalise the keep_na / keep_empty arguments for all columns (x, split_by, group_by, facet_by).

2. The split_by column is validated and its NA / empty levels are processed via process_keep_na_empty(). It is then removed from the per-column keep_na / keep_empty lists.

3. The data frame is split by split_by (preserving level order). If split_by is NULL, the data is wrapped in a single-element list with name "...".

4. Per-split palette, palcolor, legend.position, and legend.direction are resolved via check_palette(), check_palcolor(), and check_legend().

5. TrendPlotAtomic() is called for each split. If title is a function, it receives the split level name and can generate dynamic titles.

6. Results are combined via combine_plots() (when combine = TRUE) or returned as a named list.

See Also

AreaPlot for a pure stacked area plot.

Examples

data <- data.frame(
    x = factor(rep(c("A", "B", NA, "D"), 3), levels = LETTERS[1:4]),
    y = c(1, 3, 6, 5, 4, 2, 5, 7, 8, 9, 4, 8),
    group = factor(rep(c("F1", NA, "F3"), each = 4), levels = c("F1", "F2", "F3"))
)

# Basic trend plot with grouping
TrendPlot(data, x = "x", y = "y", group_by = "group")

# Scaled to proportions
TrendPlot(data, x = "x", y = "y", group_by = "group",
         scale_y = TRUE)

# Split into sub-plots (no group_by -- single-colour fill)
TrendPlot(data, x = "x", y = "y", split_by = "group")

# Per-split palettes
TrendPlot(data, x = "x", y = "y", split_by = "group",
          palette = c(F1 = "Set1", F3 = "Dark2"))

# How keep_na and keep_empty work
TrendPlot(data, x = "x", y = "y", group_by = "group",
         keep_na = TRUE, keep_empty = TRUE)
TrendPlot(data, x = "x", y = "y", group_by = "group",
         keep_na = TRUE, keep_empty = list(x = FALSE, group = 'level'))

# Faceting
TrendPlot(data, x = "x", y = "y", facet_by = "group",
         keep_na = TRUE, keep_empty = list(x = FALSE, group = 'level'))

plotthis documentation built on July 9, 2026, 5:07 p.m.