pythonnetworkxisolation

Return unconnected islands of nodes in a network with Networkx


I am using NetworkX for analyzing a network G of transport connections. After visualizing it I saw that there are some "islands" of nodes that do not have any connections to the network. Those islands mostly consist of 2 to 5 nodes. Since the network is really big I am looking for a command that returns each of those islands, preferrably in a data structure that indicates the names of the nodes. The isolates(G) command only returns nodes of degree zero, but I am interested in the islands. Is there a command for that?


Solution

  • Look into the connected_components function

    # Create three separate graphs and then compose them together.
    import networkx as nx
    G = nx.complete_graph(8)
    G2 = nx.complete_graph(range(13, 15))
    G3 = nx.complete_graph(range(16, 19))
    
    G = nx.compose_all([G, G2, G3])
    nx.draw(G)
    

    Graphs

    Using connected_components():

    list(nx.connected_components(G))
    
    [{0, 1, 2, 3, 4, 5, 6, 7}, {13, 14}, {16, 17, 18}]
    
    threshold = 6
    [c for c in nx.connected_components(G) if len(c) < threshold]
    
    [{13, 14}, {16, 17, 18}]
    

    You can also check out connected_components_subgraph