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Bars representing nodes in a Sankey diagram

Source: R/geom_node.r
geom_sankeynode.Rd

In a Sankey diagram nodes are depicted as stacked bars, possibly with vertical spacing between them. Use geom_sankeynode() to add nodes to your Sankey diagram. If you combine the nodes with geom_sankeyedge(), make sure that both use the same position object.

Usage

GeomSankeynode

geom_sankeynode(
  mapping = NULL,
  data = NULL,
  stat = "sankeynode",
  position = "sankey",
  na.rm = FALSE,
  show.legend = NA,
  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 GeomSankeynode (inherits from GeomBar, GeomRect, Geom, ggproto, gg) of length 6.

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, either as a ggproto Geom subclass or as a string naming the stat stripped of the stat_ prefix (e.g. "count" rather than "stat_count")

position

Position adjustment, either as a string naming the adjustment (e.g. "jitter" to use position_jitter), or the result of a call to a position adjustment function. Use the latter if you need to change the settings of the adjustment.

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.

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".

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.

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(). These are often aesthetics, used to set an aesthetic to a fixed value, like colour = "red" or size = 3. They may also be parameters to the paired geom/stat.

Value

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

Details

This ggplot2 layer depicts the size of all connected edges as a bar. The height of of each bar is determined by the sum of y aesthetic in each group. When the sum of edges that flow to a bar differ more than split_tol compared to the edges that flow from the same node, a vertical split is introduced in the node.

Aesthetics

geom_sankeynode() understands 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.

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")