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Graph layouts

Source: R/layout.R
layout_.Rd

This is a generic function to apply a layout function to a graph.

Usage

layout_(graph, layout, ...)

# S3 method for class 'igraph_layout_spec'
print(x, ...)

# S3 method for class 'igraph_layout_modifier'
print(x, ...)

Arguments

graph

The input graph.

layout

The layout specification. It must be a call to a layout specification function.

...

Further modifiers, see a complete list below. For the print() methods, it is ignored.

x

The layout specification

Value

The return value of the layout function, usually a two column matrix. For 3D layouts a three column matrix.

Details

There are two ways to calculate graph layouts in igraph. The first way is to call a layout function (they all have prefix layout_() on a graph, to get the vertex coordinates.

The second way (new in igraph 0.8.0), has two steps, and it is more flexible. First you call a layout specification function (the one without the layout_() prefix, and then layout_() (or add_layout_()) to perform the layouting.

The second way is preferred, as it is more flexible. It allows operations before and after the layouting. E.g. using the component_wise() argument, the layout can be calculated separately for each component, and then merged to get the final results.

Modifiers

Modifiers modify how a layout calculation is performed. Modifiers are applied in the order they are specified as arguments to layout_().

There are two types of modifiers:

  • Pre-layout modifiers affect how the layout is calculated. Only one pre-layout modifier can be used at a time.

  • Post-layout modifiers transform the resulting coordinates. Multiple post-layout modifiers can be chained together.

Currently implemented modifiers:

  • component_wise() (pre-layout) calculates the layout separately for each component of the graph, and then merges them.

  • normalize() (post-layout) scales the layout to a square.

Custom modifiers can be created using the layout_modifier() function. A custom modifier must specify:

  • id: A unique identifier string for the modifier

  • type: Either "pre" for pre-layout or "post" for post-layout

  • args: A list of arguments to pass to the apply function

  • apply: A function with signature function(graph, layout, modifier_args) that performs the modification. For pre-layout modifiers, layout is the layout specification. For post-layout modifiers, layout is the coordinate matrix to transform.

See also

add_layout_() to add the layout to the graph as an attribute.

Other graph layouts: add_layout_(), component_wise(), layout_as_bipartite(), layout_as_star(), layout_as_tree(), layout_in_circle(), layout_nicely(), layout_on_grid(), layout_on_sphere(), layout_randomly(), layout_with_dh(), layout_with_fr(), layout_with_gem(), layout_with_graphopt(), layout_with_kk(), layout_with_lgl(), layout_with_mds(), layout_with_sugiyama(), merge_coords(), norm_coords(), normalize()

Examples

g <- make_ring(10) + make_full_graph(5)
coords <- layout_(g, as_star())
plot(g, layout = coords)


# Using modifiers
g <- make_ring(10) + make_ring(5)
coords <- layout_(g, in_circle(), component_wise(), normalize())
plot(g, layout = coords)


# Creating a custom post-layout modifier
scale_by <- function(factor) {
  layout_modifier(
    id = "scale_by",
    type = "post",
    args = list(factor = factor),
    apply = function(graph, layout, modifier_args) {
      layout * modifier_args$factor
    }
  )
}
coords <- layout_(make_ring(10), in_circle(), scale_by(3))
plot(make_ring(10), layout = coords)