python networkx remove nodes and edges with some condition

Question

In the python library networkx I would like to remove the nodes and edges of a graph which have some property. For example, suppose I wanted to remove all nodes and edges where

Answer 1

Note that in Aric's for networkx==2.2, you need to wrap G.degree() in a dictionary because the networkx view object doesn't have an items method. This line would be:

[node for node,degree in dict(G.degree()).items() if degree > 2]

Answer 2

The Graph.remove_nodes_from() method takes a list (container actually) of nodes. So you just need to create a list that satisfies your condition. You can use Python's list comprehension structure to compactly create a list of nodes to delete.

In [1]: import networkx as nx

In [2]: G = nx.Graph()

In [3]: G.add_edge(1,2)

In [4]: G.add_edge(1,3)

In [5]: G.add_edge(1,4)

In [6]: G.add_edge(2,3)

In [7]: G.add_edge(2,4)

In [8]: G.degree()
Out[8]: {1: 3, 2: 3, 3: 2, 4: 2}

In [9]: remove = [node for node,degree in dict(G.degree()).items() if degree > 2]

In [10]: remove
Out[10]: [1, 2]

In [11]: G.nodes()
Out[11]: [1, 2, 3, 4]

In [12]: G.remove_nodes_from(remove)

In [13]: G.nodes()
Out[13]: [3, 4]

Answer 3

If we have an initialized graph g the following will set f to be g subject to the constraint that each vertex must have a degree > 0. We could easily generalize 0 with a variable:

f = nx.Graph()                                                                                                                                     
fedges = filter(lambda x: g.degree()[x[0]] > 0 and g.degree()[x[1]] > 0, g.edges())
f.add_edges_from(fedges)