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Sankey edges (flows)

Source: R/geom_segment.r, R/geom_edge.r
geom_sankeyedge.Rd

geom_sankeysegment() draws a straight line between two connected nodes, geom_sankeyedge() draws a ribbon between nodes following a Bezier curved path. If you combine the edges with geom_sankeynode(), make sure that both use the same position object.

Usage

GeomSankeysegment

geom_sankeysegment(
  mapping = NULL,
  data = NULL,
  stat = "sankeyedge",
  position = "sankey",
  na.rm = FALSE,
  show.legend = NA,
  order = c("ascending", "descending", "as_is"),
  width = "auto",
  align = c("bottom", "top", "center", "justify"),
  h_space = "auto",
  v_space = 0,
  nudge_x = 0,
  nudge_y = 0,
  split_nodes = FALSE,
  split_tol = 0.001,
  direction = c("forward", "backward"),
  inherit.aes = TRUE,
  ...
)

GeomSankeyedge

geom_sankeyedge(
  mapping = NULL,
  data = NULL,
  stat = "sankeyedge",
  position = "sankey",
  na.rm = FALSE,
  show.legend = NA,
  slope = 0.5,
  ncp = 100,
  width = "auto",
  align = c("bottom", "top", "center", "justify"),
  order = c("ascending", "descending", "as_is"),
  h_space = "auto",
  v_space = 0,
  nudge_x = 0,
  nudge_y = 0,
  split_nodes = FALSE,
  split_tol = 0.001,
  direction = c("forward", "backward"),
  inherit.aes = TRUE,
  ...
)

Format

An object of class GeomSankeysegment (inherits from GeomSegment, Geom, ggproto, gg) of length 4.

An object of class GeomSankeyedge (inherits from GeomSankeysegment, GeomSegment, Geom, ggproto, gg) of length 7.

Arguments

mapping

Set of aesthetic mappings created by 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. 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)).

stat

The statistical transformation to use on the data for this layer. When using a geom_*() function to construct a layer, the stat argument can be used the override the default coupling between geoms and stats. The stat argument accepts the following:

  • A Stat ggproto subclass, for example StatCount.

  • A string naming the stat. To give the stat as a string, strip the function name of the stat_ prefix. For example, to use stat_count(), give the stat as "count".

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

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.

na.rm

If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.

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. It can also be a named logical vector to finely select the aesthetics to display.

order

A character indicating the method to be used for the order of stacking nodes and edges in a plot. Should be one of: ascending (default), sorts nodes and edges from large to small (largest on top); descending sorts nodes and edges from small to large (smallest on top); as_is will leave the order of nodes and edges as they are in data.

width

Width of the node (numeric). When split_nodes is set to TRUE each part of the split node will have half this width. Use "auto" to automatically determine a suitable width.

align

A character that indicates how the nodes across the stages are aligned. It can be any of "top", "bottom", "center" or "justify".

h_space

Horizontal space between split nodes (numeric). This argument is ignored when split_nodes == FALSE. Use "auto" to automatically position split nodes.

v_space

Vertical space between nodes (numeric). When set to zero (0), the Sankey diagram becomes an alluvial plot. Use "auto" to automatically determine a suitable vertical space.

nudge_x, nudge_y

Horizontal and vertical adjustment to nudge items by. Can be useful for offsetting labels.

split_nodes

A logical value indicating whether the source and destination nodes should be depicted as separate boxes.

split_tol

When the relative node size (resulting source and destination edges) differs more than this fraction, the node will be displayed as two separate bars.

direction

One of "forward" (default) or "backward". When set to "backward" the direction of the edges will be inverted. In most cases this parameter won't affect the plot. It can be helpful when you want to decorate the end of an edge (instead of the start; see examples).

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. borders().

...

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.

slope

Slope parameter (numeric) for the Bezier curves used to depict the edges. Any value between 0 and 1 will work nicely. Other non-zero values will also work.

ncp

Number of control points on the Bezier curve that forms the edge. Larger numbers will result in smoother curves, but cost more computational time. Default is 100.

Value

Returns a ggplot2::layer() which can be added to a ggplot2::ggplot()

Details

This ggplot2 layer connects between paired nodes via a Bezier curve. The width of the curve is determined by its y aesthetic. It will be attempted to keep the width of the curve constant along its curved path, for the targeted graphics device. When the aspect ratio of the graphics device is altered after the plot is generated, the aspect ratio maybe off. In that case render the plot again.

Aesthetics

geom_sankeysegment() and geom_sankeyedge() understand the following aesthetics (required aesthetics are in bold)

Important aspects

  • x: Works for variables on a discrete scale. Might work for continuous variables but is not guaranteed. This variable is used to distinguish between stages in the Sankey diagram on the x axis.

  • y: A continuous variable representing the width of the edges in a Sankey diagram.

  • group: A discrete variable used for grouping edges to nodes in each stage. Essentially it is an identifier for the nodes.

  • connector: Indicates which side of an edge is reflected by the corresponding record. Should be one of "from" or "to".

  • edge_id: A unique identifier value for each edge. This identifier is used to link specific "from" and "to" records in an edge (flow).

  • fill: see vignette("ggplot2-specs", "ggplot2")

  • colour: see vignette("ggplot2-specs", "ggplot2")

  • linetype: see vignette("ggplot2-specs", "ggplot2")

  • linewidth: see vignette("ggplot2-specs", "ggplot2")

  • alpha: A variable to control the opacity of an element.

  • waist: A variable to control the width of an edge in between two nodes. Small values will create a hour glass shape, whereas large values will produce an apple shape.

Author

Pepijn de Vries

Examples

library(ggplot2)
data("ecosystem_services")

ggplot(ecosystem_services_pivot1, aes(x = stage, y = RCSES, group = node,
                    connector = connector, edge_id = edge_id,
                    fill = node)) +
  geom_sankeynode(v_space = "auto") +
  geom_sankeyedge(v_space = "auto")