(igraph) Grouped layout based on attribute

Question

I\'m using the iGraph package in R to layout a network graph, and I would like to group the vertex coordinates based on attribute values.

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Answer 1

While this question is rather old, it is a reasonable question and deserves an answer.

No data was provided so I will generate an arbitrary example.

library(igraph)
set.seed(1234)
G = erdos.renyi.game(20, 0.25)
V(G)$Group1 = sample(3,20, replace=TRUE)
plot(G, vertex.color=rainbow(3, alpha=0.4)[V(G)$Group1])

Without doing anything, the Group is ignored.

Now, we need to create a layout that will plot nodes in the same group close together. We can do this by creating a graph with the same nodes, but with additional links between nodes in the same group. The within-group links will be given a high weight and the original links will be given a small weight. This will cluster nodes in the same group. We then apply the layout to plotting the original graph, without the extra links. They were just to get a good layout.

G_Grouped = G
E(G_Grouped)$weight = 1

## Add edges with high weight between all nodes in the same group
for(i in unique(V(G)$Group1)) {
    GroupV = which(V(G)$Group1 == i)
    G_Grouped = add_edges(G_Grouped, combn(GroupV, 2), attr=list(weight=5))
} 

## Now create a layout based on G_Grouped
set.seed(567)
LO = layout_with_fr(G_Grouped)

## Use the layout to plot the original graph
plot(G, vertex.color=rainbow(3, alpha=0.4)[V(G)$Group1], layout=LO)

If you want to go beyond this to have multiple levels of grouping, just add additional links with appropriate weights to connect the subgroups too.