scale_node_positions: Scale node positions in an 'igraph' object

In GephiForR: 'Gephi' Network Visualization

Scale node positions in an igraph object

Description

This function scales the positions of nodes in a graph relative to their centroid; compatible with expansions and contractions.

Usage

scale_node_positions(layout, scale_factor = 1.2)

Arguments

layout	A 2-column matrix representing the position data, where the columns are the x- and y-coordinates of each node, respectively.
scale_factor	A numeric value indicating the factor by which to scale the node positions. The default is scale_factor = 1.2.

Details

This function expands or contracts the graph around a centroid, facilitating visualization. Factors greater than 1 expand the network around the centroid while those less than 1 contract it around the centroid. scale_factor = 1 is no change. Note that unscaled plot commands like plot(g, layout = layout_expanded) make the change difficult to see, so scaled plots are recommended for comparison.

Value

A matrix of updated node positions.

Examples

  set.seed(10)
  library(igraph)

  # Generating graph and setting initial layout
  g <- erdos.renyi.game(100, 0.05)
  layout <- layout_with_fr(g)

  # Plotting original graph, maintaining fixed scale so expansion is clear
  plot(layout, main="Original Graph", xlab="", ylab="", xlim=c(-20, 15), ylim=c(-20, 15))

  # Expanding node positions
  layout_expanded <- scale_node_positions(layout, 2)

  # Plotting expanded graph, maintaining fixed scale so expansion is clear
  plot(layout_expanded, main="Expanded Graph", xlab="", ylab="", xlim=c(-20, 15), ylim=c(-20, 15))

  # Contract node positions
  layout_cont <- scale_node_positions(layout, 0.8)

  # Plotting contracted graph, maintaining fixed scale so transformation is clear
  plot(layout_cont, main="Contracted Graph", xlab="", ylab="", xlim=c(-20, 15), ylim=c(-20, 15))


  # Note that igraph plots like below make it difficult to see the transformation,
  # because they are autoscaled.
  # plot(g, layout = layout_expanded)
  # The change is easy to see in scaled plots, as shown.

GephiForR documentation built on Sept. 11, 2024, 8:05 p.m.