CODEWITHSUNDEEP
rigraph
Leosar
Leosar

Reputation: 2072

Get a graph from all vertex with incident edges R igraph

I would like to obtain a subgraph from a graph, composed of all the vertex with incident edges starting from some vertices, and following the edges until there are no more incident edges. With the following code I only get the first neighbours

g <-   graph_from_literal( 1 -+ 4 -+ 5 -+ 8,2 -+ 5 , 3-+6-+7,  4+-3, 4-+8, 5 -+9, simplify = FALSE)
adjacent_vertices(g, V(g)[c("7","9")], mode="in")

I know that I should make some kind of loop but adjacent_vertices returns a list and I can't figure out how to make it.

For this example, the result should be

graph_from_literal( 1 -+ 4 -+ 5 ,2 -+ 5 , 3-+6-+7,  4+-3, 5 -+9, simplify = FALSE)

Upvotes: 1

Views: 387

Answers (1)

user20650
user20650

Reputation: 25864

make_ego_graph can be used to find subgraphs in the neighbourhood of specific nodes. You can search through the full graph by setting the order parameter in the function make_ego_graph.

Example

library(igraph)

# Your graph
g = graph_from_literal( 1 -+ 4 -+ 5 -+ 8, 2 -+ 5 , 3-+6-+7, 4+-3, 4-+8, 5 -+9, 
                        simplify = FALSE)

# Set the order equal to the number of nodes in the graph    
sg = make_ego_graph(g, nodes = V(g)[c("7","9")], order=length(V(g)), mode="in")

# This returns two subgraphs as node 3 has no inward edges and so the graph 3->6->7 
# is unconnected to the other nodes. You can join the subgraphs by using 
do.call(union, sg)

Upvotes: 1

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