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Create polygonal regions in a ternary plot based on a reference point

Source: R/geom_ternary_region.R
geom_ternary_region.Rd

geom_ternary_region() and stat_ternary_region() divide the ternary triangle into three polygonal regions centered around a specific reference point.

Geometrically, lines are drawn from the reference point perpendicular to the three edges of the triangle. These lines partition the simplex into three zones, where each zone is associated with the closest vertex (item). This is often used to visualize "winning regions" or catchment areas for each item.

Usage

geom_ternary_region(
  mapping = NULL,
  position = "identity",
  show.legend = NA,
  inherit.aes = FALSE,
  x1 = 1/3,
  x2 = 1/3,
  x3 = 1/3,
  vertex_labels = NULL,
  ...
)

stat_ternary_region(
  mapping = NULL,
  data = NULL,
  geom = "polygon",
  position = "identity",
  show.legend = NA,
  inherit.aes = FALSE,
  x1 = 1/3,
  x2 = 1/3,
  x3 = 1/3,
  vertex_labels = NULL,
  ...
)

StatTernaryRegion

Format

An object of class StatTernaryRegion (inherits from Stat, ggproto, gg) of length 3.

Arguments

mapping

Set of aesthetic mappings created by ggplot2::aes(). To map aesthetics to the computed region labels, use ggplot2::after_stat(), e.g., aes(fill = after_stat(vertex_labels)).

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

show.legend

Logical. Should this layer be included in the legends? NA (default) includes it if aesthetics are mapped. FALSE never includes it; TRUE always includes it.

inherit.aes

If FALSE, overrides the default aesthetics rather than combining with them.

x1, x2, x3

Numeric values defining the reference point in ternary coordinates (proportions). Must sum to 1 (or will be normalized). Default is c(1/3, 1/3, 1/3) (the centroid), which divides the space into three equal regions.

vertex_labels

Character vector of length 3 providing names for the regions. The order must correspond to the three vertices of the ternary plot. If NULL, regions are labeled "Region 1", "Region 2", and "Region 3", starting from the rightmost vertex and moving clockwise.

...

Other arguments passed on to layer()'s params argument. These arguments broadly fall into one of 4 categories below. Notably, further arguments to the position argument, or aesthetics that are required can not be passed through .... Unknown arguments that are not part of the 4 categories below are ignored.

  • Static aesthetics that are not mapped to a scale, but are at a fixed value and apply to the layer as a whole. For example, colour = "red" or linewidth = 3. The geom's documentation has an Aesthetics section that lists the available options. The 'required' aesthetics cannot be passed on to the params. Please note that while passing unmapped aesthetics as vectors is technically possible, the order and required length is not guaranteed to be parallel to the input data.

  • When constructing a layer using a stat_*() function, the ... argument can be used to pass on parameters to the geom part of the layer. An example of this is stat_density(geom = "area", outline.type = "both"). The geom's documentation lists which parameters it can accept.

  • Inversely, when constructing a layer using a geom_*() function, the ... argument can be used to pass on parameters to the stat part of the layer. An example of this is geom_area(stat = "density", adjust = 0.5). The stat's documentation lists which parameters it can accept.

  • The key_glyph argument of layer() may also be passed on through .... This can be one of the functions described as key glyphs, to change the display of the layer in the legend.

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. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

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. A function can be created from a formula (e.g. ~ head(.x, 10)).

geom

The geometric object to use to display the data. Default is "polygon".

Computed variables

stat_ternary_region() calculates the following variables which can be accessed with after_stat():

x, y

Cartesian coordinates defining the polygon shapes.

id

Numeric identifier for the specific geometric points used to build the polygons:

  • 1-3: The main vertices of the ternary triangle.

  • 4: The reference point (center).

  • 5-7: The projection points on the edges.

group

Integer (1, 2, or 3) identifying which region the polygon belongs to.

vertex_labels

The label assigned to the region (derived from the vertex_labels parameter).

Examples

library(ggplot2)
aecdop22_transformed <- prefviz:::aecdop22_transformed

# Get ternable
tern22 <- as_ternable(aecdop22_transformed, ALP:Other)

# Draw the ternary plot
ggplot(get_tern_data(tern22, plot_type = "2D"), aes(x = x1, y = x2)) +
  add_ternary_base() +
  geom_ternary_region(
    vertex_labels = tern22$vertex_labels,
    aes(fill = after_stat(vertex_labels)), 
    alpha = 0.3, color = "grey50",
    show.legend = FALSE
  )