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subgraph

Extract subgraph

Syntax

H = subgraph(G,nodeIDs)
H = subgraph(G,idx)

Description

example

H = subgraph(G,nodeIDs) returns a subgraph of G that contains only the nodes specified by nodeIDs.

H = subgraph(G,idx) specifies the subgraph nodes using a logical vector.

Examples

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Create and plot a graph.

s = [1 1 1 1 2 2 2 2 2 2 2 2 2 2 15 15 15 15 15];
t = [3 5 4 2 14 6 11 12 13 10 7 9 8 15 16 17 19 18 20];
G = graph(s,t);
plot(G,'Layout','force')

Extract a subgraph from G by specifying which nodes to include. The node numbering in the subgraph is reset.

idx = [2 15 16 17 18 19 20 1 3 4 5];
H = subgraph(G,idx);
plot(H,'Layout','force')

Create and plot a weighted graph with named nodes.

s = [1 1 1 2 2 2 8 8 8 8];
t = [2 3 4 5 6 7 9 10 11 12];
weights = [10 30 40 80 60 60 20 30 90 80];
names = {'A' 'B' 'C' 'D' 'E' 'F' 'G' 'H' 'I' 'J' 'K' 'L'};
G = graph(s,t,weights,names);
plot(G,'EdgeLabel',G.Edges.Weight)

Extract a subgraph that contains node 'B' and all of its neighbors. subgraph preserves the node names and edge weights. However, the numeric node IDs in H are renumbered compared to G.

N = neighbors(G,'B');
H = subgraph(G, ['B'; N]);
plot(H,'EdgeLabel',H.Edges.Weight)

Input Arguments

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Input graph, specified as either a graph or digraph object. Use graph to create an undirected graph or digraph to create a directed graph.

Example: G = graph(1,2)

Example: G = digraph([1 2],[2 3])

Node IDs, specified as a vector of indices, or cell array of node names. nodeIDs selects a subset of the nodes in G to generate the subgraph, H.

Example: H = subgraph(G,[1 2 5])

Example: H = subgraph(G,{'A' 'B' 'E'})

Node selection vector, specified as a logical vector. The subgraph contains only the nodes J for which idx(J) is logical 1 (true). The index of node J in H is I(J), where I = find(idx).

Example: subgraph(G,degree(G)>2)

Data Types: logical

Output Arguments

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Subgraph, returned as a graph or digraph object. H contains only the nodes that were selected with nodeIDs or idx. Other nodes in G (and the edges connecting to those nodes) are discarded. The node properties and edge properties of the selected nodes and edges are carried over from G into H.

See graph or digraph for more information about graph objects.

Introduced in R2015b

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