R: Draw edges as Arcs

geom_edge_arc {ggraph} | R Documentation

## Draw edges as Arcs

### Description

This geom is mainly intended for arc linear and circular diagrams (i.e. used together with `layout_igraph_linear`), though it can be used elsewere. It draws edges as arcs with a hight proportional to the distance between the nodes. Arcs are calculated as beziers. For linear layout the placement of control points are related to the `curvature` argument and the distance between the two nodes. For circular layout the control points are placed on the same angle as the start and end node at a distance related to the distance between the nodes.

### Usage

    geom_edge_arc(mapping = NULL, data = get_edges(), position = "identity",
      arrow = NULL, curvature = 1, n = 100, fold = FALSE,
      lineend = "butt", linejoin = "round", linemitre = 1,
      label_colour = "black", label_alpha = 1, label_parse = FALSE,
      check_overlap = FALSE, angle_calc = "rot", force_flip = TRUE,
      label_dodge = NULL, label_push = NULL, show.legend = NA, ...)

    geom_edge_arc2(mapping = NULL, data = get_edges("long"),
      position = "identity", arrow = NULL, curvature = 1, n = 100,
      fold = FALSE, lineend = "butt", linejoin = "round", linemitre = 1,
      label_colour = "black", label_alpha = 1, label_parse = FALSE,
      check_overlap = FALSE, angle_calc = "rot", force_flip = TRUE,
      label_dodge = NULL, label_push = NULL, show.legend = NA, ...)

    geom_edge_arc0(mapping = NULL, data = get_edges(), position = "identity",
      arrow = NULL, curvature = 1, lineend = "butt", show.legend = NA,
      fold = fold, ...)

### Arguments

`mapping` | Set of aesthetic mappings created by `aes` or `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 return of a call to `get_edges()` or a data.frame giving edges in corrent format (see details for for guidance on the format). See `get_edges` for more details on edge extraction.
`position` | Position adjustment, either as a string, or the result of a call to a position adjustment function.
`arrow` | Arrow specification, as created by `grid::arrow()`.
`curvature` | The bend of the curve. 1 approximates a halfcircle while 0 will give a straight line. Negative number will change the direction of the curve. Only used if `circular = FALSE`.
`n` | The number of points to create along the path.
`fold` | Logical. Should arcs appear on the same side of the nodes despite different directions. Default to `FALSE`.
`lineend` | Line end style (round, butt, square).
`linejoin` | Line join style (round, mitre, bevel).
`linemitre` | Line mitre limit (number greater than 1).
`label_colour` | The colour of the edge label. If `NA` it will use the colour of the edge.
`label_alpha` | The opacity of the edge label. If `NA` it will use the opacity of the edge.
`label_parse` | If `TRUE`, the labels will be parsed into expressions and displayed as described in `plotmath`.
`check_overlap` | If `TRUE`, text that overlaps previous text in the same layer will not be plotted.
`angle_calc` | Either 'none', 'along', or 'across'. If 'none' the label will use the angle aesthetic of the geom. If 'along' The label will be written along the edge direction. If 'across' the label will be written across the edge direction.
`force_flip` | Logical. If `angle_calc` is either 'along' or 'across' should the label be flipped if it is on it's head. Default to `TRUE`.
`label_dodge` | A `unit` giving a fixed vertical shift to add to the label in case of `angle_calc` is either 'along' or 'across'
`label_push` | A `unit` giving a fixed horizontal shift to add to the label in case of `angle_calc` is either 'along' or 'across'
`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.
`...` | Other arguments passed on to `layer()`. These are often aesthetics, used to set an aesthetic to a fixed value, like `color = "red"` or `size = 3`. They may also be parameters to the paired geom/stat.

### Details

Many geom_edge_* layers comes in 3 flavors depending on the level of control needed over the drawing. The default (no numeric postfix) generate a number of points (`n`) along the edge and draws it as a path. Each point along the line has a numeric value associated with it giving the position along the path, and it is therefore possible to show the direction of the edge by mapping to this e.g. `colour = ..index..`. The version postfixed with a "2" uses the "long" edge format (see `get_edges`) and makes it possible to interpolate node parameter between the start and end node along the edge. It is considerable less performant so should only be used if this is needed. The version postfixed with a "0" draws the edge in the most performant way, often directly using an appropriate grob from the grid package, but does not allow for gradients along the edge.

Often it is beneficial to stop the drawing of the edge before it reaches the node, for instance in cases where an arrow should be drawn and the arrowhead shouldn't lay ontop or below the node point. geom_edge_* and geom_edge_*2 supports this through the start_cap and end_cap aesthetics that takes a `geometry` specification and dynamically caps the termini of the edges based on the given specifications. This means that if `end_cap = circle(1, 'cm')` the edges will end at a distance of 1cm even during resizing of the plot window.

All `geom_edge_*` and `geom_edge_*2` have the ability to draw a label along the edge. The reason this is not a separate geom is that in order for the label to know the location of the edge it needs to know the edge type etc. Labels are drawn by providing a label aesthetic. The label_pos can be used to specify where along the edge it should be drawn by supplying a number between 0 and 1. The label_size aesthetic can be used to control the size of the label. Often it is needed to have the label written along the direction of the edge, but since the actual angle is dependent on the plot dimensions this cannot be calculated beforehand. Using the angle_calc argument allows you to specify whether to use the supplied angle aesthetic or whether to draw the label along or across the edge.

### Aesthetics

geom_edge_arc and geom_edge_arc0 understand the following aesthetics. Bold aesthetics are automatically set, but can be overridden.

- x

- y

- xend

- yend

- circular

- edge_colour

- edge_width

- edge_linetype

- edge_alpha

- filter

geom_edge_arc2 understand the following aesthetics. Bold aesthetics are automatically set, but can be overridden.

- x

- y

- group

- circular

- edge_colour

- edge_width

- edge_linetype

- edge_alpha

- filter

geom_edge_arc and geom_edge_arc2 furthermore takes the following aesthetics.

- start_cap

- end_cap

- label

- label_pos

- label_size

- angle

- hjust

- vjust

- family

- fontface

- lineheight

### Computed variables

index

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

### 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.

### Author(s)

Thomas Lin Pedersen

### See Also

Other geom_edge_*: `geom_edge_density`, `geom_edge_diagonal`, `geom_edge_elbow`, `geom_edge_fan`, `geom_edge_hive`, `geom_edge_link`, `geom_edge_loop`

### Examples

    require(igraph)
    # Make a graph with different directions of edges
    gr <- graph_from_edgelist(
      t(apply(as_edgelist(make_graph('Meredith')), 1, sample))
    )
    E(gr)$class <- sample(letters[1:3], gsize(gr), replace = TRUE)
    V(gr)$class <- sample(letters[1:3], gorder(gr), replace = TRUE)

    ggraph(gr, 'linear') +
      geom_edge_arc(aes(alpha = ..index..))

    ggraph(gr, 'linear') +
      geom_edge_arc2(aes(colour = node.class), curvature = 0.6)

    ggraph(gr, 'linear', circular = TRUE) +
      geom_edge_arc0(aes(colour = class))

[Package ggraph version 1.0.2 Index]