% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/trendplot.R
\name{TrendPlot}
\alias{TrendPlot}
\title{Trend plot}
\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{
\item{data}{A data frame.}

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

\item{y}{A character string specifying the column name of the data frame to plot for the y-axis.}

\item{x_sep}{A character string used to join multiple \code{x} columns.
Default \code{"_"}. Ignored when \code{x} is a single column.}

\item{split_by}{The column(s) to split the data by and produce separate
sub-plots. Multiple columns are concatenated with \code{split_by_sep}.}

\item{split_by_sep}{A character string to separate concatenated
\code{split_by} columns. Default \code{"_"}.}

\item{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 \code{group_by_sep} as the separator}

\item{group_by_sep}{The separator for multiple group_by columns. See \code{group_by}}

\item{group_name}{A character string used as the fill legend title.
When \code{NULL}, the \code{group_by} column name is used.}

\item{scale_y}{A logical value. When \code{TRUE}, y-values are scaled to
proportions within each (\code{x}, \code{facet_by}) group so that each
x position stacks to 1.0. The y-axis labels switch from numeric to
percent format automatically.}

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

\item{theme_args}{A list of arguments to pass to the theme function.}

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

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

\item{palreverse}{A logical value indicating whether to reverse the palette. Default is FALSE.}

\item{alpha}{A numeric value specifying the transparency of the plot.}

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

\item{facet_scales}{Whether to scale the axes of facets. Default is "fixed"
Other options are "free", "free_x", "free_y". See \code{ggplot2::facet_wrap}}

\item{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.}

\item{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.}

\item{facet_byrow}{A logical value indicating whether to fill the plots by row. Default is TRUE.}

\item{x_text_angle}{A numeric value specifying the angle of the x-axis text.}

\item{aspect.ratio}{A numeric value specifying the aspect ratio of the plot.}

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

\item{legend.direction}{A character string specifying the direction of the legend.}

\item{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.}

\item{subtitle}{A character string specifying the subtitle of the plot.}

\item{xlab}{A character string specifying the x-axis label.}

\item{ylab}{A character string specifying the y-axis label.}

\item{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 \code{x}, \code{group_by}, \code{fill_by}, etc.}

\item{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 \code{x}, \code{group_by}, \code{fill_by}, etc.
\itemize{
\item{\code{FALSE} (default): Drop empty factor levels from the data before plotting.}
\item{\code{TRUE}: Keep empty factor levels and show them as a separate category in the plot.}
\item{\code{"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: \code{levels}}
}}

\item{seed}{A numeric seed for reproducibility. Passed to
\code{\link{validate_common_args}()}.}

\item{combine}{Logical; when \code{TRUE} (default), returns a combined
\code{patchwork} object. When \code{FALSE}, returns a named list of
individual \code{ggplot} objects.}

\item{ncol, nrow}{Integer number of columns / rows for the combined layout
(passed to \code{\link[patchwork]{wrap_plots}}).}

\item{byrow}{Logical; fill the combined layout by row. Default \code{TRUE}
(passed to \code{\link[patchwork]{wrap_plots}}).}

\item{axes}{A character string specifying how axes should be treated across
the combined layout (passed to \code{\link[patchwork]{wrap_plots}}).}

\item{axis_titles}{A character string specifying how axis titles should be
treated across the combined layout. Defaults to \code{axes}.}

\item{guides}{A character string specifying how guides (legends) should be
collected across panels. Default \code{"collect"} (passed to
\code{\link{combine_plots}()}).}

\item{design}{A custom layout design for the combined plot (passed to
\code{\link{combine_plots}()}).}

\item{...}{Additional arguments.}
}
\value{
A \code{ggplot} object, a \code{patchwork} object, or a named list
of \code{ggplot} objects (when \code{combine = FALSE}), each with
\code{height} and \code{width} attributes in inches.
}
\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 \strong{count aggregation} (omit \code{y} to plot
observation counts per x-category), \strong{proportion scaling}
(\code{scale_y = TRUE} normalises each x position to 100\\%), per-group
colour control, faceting, and splitting into separate sub-plots via
\code{split_by}.
}
\section{split_by workflow}{

When \code{split_by} is provided:
\enumerate{
\item \code{\link{check_keep_na}()} and \code{\link{check_keep_empty}()}
normalise the \code{keep_na} / \code{keep_empty} arguments for all
columns (\code{x}, \code{split_by}, \code{group_by}, \code{facet_by}).
\item The \code{split_by} column is validated and its NA / empty levels
are processed via \code{\link{process_keep_na_empty}()}. It is
then removed from the per-column \code{keep_na} / \code{keep_empty}
lists.
\item The data frame is split by \code{split_by} (preserving level
order). If \code{split_by} is \code{NULL}, the data is wrapped in
a single-element list with name \code{"..."}.
\item Per-split \code{palette}, \code{palcolor},
\code{legend.position}, and \code{legend.direction} are resolved
via \code{\link{check_palette}()}, \code{\link{check_palcolor}()},
and \code{\link{check_legend}()}.
\item \code{\link{TrendPlotAtomic}()} is called for each split. If
\code{title} is a function, it receives the split level name and
can generate dynamic titles.
\item Results are combined via \code{\link{combine_plots}()} (when
\code{combine = TRUE}) or returned as a named list.
}
}

\examples{
\donttest{
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'))
}
}
\seealso{
\code{\link{AreaPlot}} for a pure stacked area plot.
}
