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1"""
2Functions for identifying isolate (degree zero) nodes.
3"""
5import networkx as nx
7__all__ = ["is_isolate", "isolates", "number_of_isolates"]
10@nx._dispatchable
11def is_isolate(G, n):
12 """Determines whether a node is an isolate.
14 An *isolate* is a node with no neighbors (that is, with degree
15 zero). For directed graphs, this means no in-neighbors and no
16 out-neighbors.
18 Parameters
19 ----------
20 G : NetworkX graph
22 n : node
23 A node in `G`.
25 Returns
26 -------
27 is_isolate : bool
28 True if and only if `n` has no neighbors.
30 Examples
31 --------
32 >>> G = nx.Graph()
33 >>> G.add_edge(1, 2)
34 >>> G.add_node(3)
35 >>> nx.is_isolate(G, 2)
36 False
37 >>> nx.is_isolate(G, 3)
38 True
39 """
40 return G.degree(n) == 0
43@nx._dispatchable
44def isolates(G):
45 """Iterator over isolates in the graph.
47 An *isolate* is a node with no neighbors (that is, with degree
48 zero). For directed graphs, this means no in-neighbors and no
49 out-neighbors.
51 Parameters
52 ----------
53 G : NetworkX graph
55 Returns
56 -------
57 iterator
58 An iterator over the isolates of `G`.
60 Examples
61 --------
62 To get a list of all isolates of a graph, use the :class:`list`
63 constructor::
65 >>> G = nx.Graph()
66 >>> G.add_edge(1, 2)
67 >>> G.add_node(3)
68 >>> list(nx.isolates(G))
69 [3]
71 To remove all isolates in the graph, first create a list of the
72 isolates, then use :meth:`Graph.remove_nodes_from`::
74 >>> G.remove_nodes_from(list(nx.isolates(G)))
75 >>> list(G)
76 [1, 2]
78 For digraphs, isolates have zero in-degree and zero out_degre::
80 >>> G = nx.DiGraph([(0, 1), (1, 2)])
81 >>> G.add_node(3)
82 >>> list(nx.isolates(G))
83 [3]
85 """
86 return (n for n, d in G.degree() if d == 0)
89@nx._dispatchable
90def number_of_isolates(G):
91 """Returns the number of isolates in the graph.
93 An *isolate* is a node with no neighbors (that is, with degree
94 zero). For directed graphs, this means no in-neighbors and no
95 out-neighbors.
97 Parameters
98 ----------
99 G : NetworkX graph
101 Returns
102 -------
103 int
104 The number of degree zero nodes in the graph `G`.
106 """
107 return sum(1 for v in isolates(G))