Create hierarchical edge bundles between node connections

Source: R/geom_conn_bundle.R

Hierarchical edge bundling is a technique to introduce some order into the hairball structure that can appear when there's a lot of overplotting and edge crossing in a network plot. The concept requires that the network has an intrinsic hierarchical structure that defines the layout but is not shown. Connections between points (that is, not edges) are then drawn so that they loosely follows the underlying hierarchical structure. This results in a flow-like structure where lines that partly move in the same direction will be bundled together.

geom_conn_bundle(
  mapping = NULL,
  data = get_con(),
  position = "identity",
  arrow = NULL,
  lineend = "butt",
  show.legend = NA,
  n = 100,
  tension = 0.8,
  ...
)

geom_conn_bundle2(
  mapping = NULL,
  data = get_con(),
  position = "identity",
  arrow = NULL,
  lineend = "butt",
  show.legend = NA,
  n = 100,
  tension = 0.8,
  ...
)

geom_conn_bundle0(
  mapping = NULL,
  data = get_con(),
  position = "identity",
  arrow = NULL,
  lineend = "butt",
  show.legend = NA,
  tension = 0.8,
  ...
)

Arguments

mapping

Set of aesthetic mappings created by ggplot2::aes() or ggplot2::aes_(). By default x, y, xend, yend, group and circular are mapped to x, y, xend, yend, edge.id and circular in the edge data.

data

The result of a call to get_con()

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.

arrow

Arrow specification, as created by grid::arrow().

lineend

Line end style (round, butt, square).

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. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

n

The number of points to create along the path.

tension

How "loose" should the bundles be. 1 will give very tight bundles, while 0 will turn of bundling completely and give straight lines. Defaults to 0.8

...

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.

Note

In order to avoid excessive typing edge aesthetic names are automatically expanded. Because of this it is not necessary to write edge_colour within the aes() call as colour will automatically be renamed appropriately.

Aesthetics

geom_conn_bundle* understands the following aesthetics. Bold aesthetics are automatically set, but can be overwritten.

  • x

  • y

  • group

  • circular

  • edge_colour

  • edge_width

  • edge_linetype

  • edge_alpha

  • filter

Computed variables

index

The position along the path (not computed for the *0 version)

References

Holten, D. (2006). Hierarchical edge bundles: visualization of adjacency relations in hierarchical data. IEEE Transactions on Visualization and Computer Graphics, 12(5), 741-748. doi:10.1109/TVCG.2006.147

Author

Thomas Lin Pedersen

Examples

# Create a graph of the flare class system
library(tidygraph)
flareGraph <- tbl_graph(flare$vertices, flare$edges) %>%
  mutate(
    class = map_bfs_chr(node_is_root(), .f = function(node, dist, path, ...) {
      if (dist <= 1) {
        return(shortName[node])
      }
      path$result[[nrow(path)]]
    })
  )
importFrom <- match(flare$imports$from, flare$vertices$name)
importTo <- match(flare$imports$to, flare$vertices$name)

# Use class inheritance for layout but plot class imports as bundles
ggraph(flareGraph, 'dendrogram', circular = TRUE) +
  geom_conn_bundle(aes(colour = after_stat(index)),
    data = get_con(importFrom, importTo),
    edge_alpha = 0.25
  ) +
  geom_node_point(aes(filter = leaf, colour = class)) +
  scale_edge_colour_distiller('', direction = 1, guide = 'edge_direction') +
  coord_fixed() +
  ggforce::theme_no_axes()