108 lines
2.3 KiB
Python
108 lines
2.3 KiB
Python
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"""
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Functions for identifying isolate (degree zero) nodes.
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"""
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import networkx as nx
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__all__ = ["is_isolate", "isolates", "number_of_isolates"]
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@nx._dispatchable
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def is_isolate(G, n):
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"""Determines whether a node is an isolate.
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An *isolate* is a node with no neighbors (that is, with degree
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zero). For directed graphs, this means no in-neighbors and no
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out-neighbors.
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Parameters
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----------
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G : NetworkX graph
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n : node
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A node in `G`.
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Returns
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-------
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is_isolate : bool
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True if and only if `n` has no neighbors.
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Examples
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--------
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>>> G = nx.Graph()
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>>> G.add_edge(1, 2)
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>>> G.add_node(3)
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>>> nx.is_isolate(G, 2)
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False
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>>> nx.is_isolate(G, 3)
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True
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"""
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return G.degree(n) == 0
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@nx._dispatchable
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def isolates(G):
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"""Iterator over isolates in the graph.
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An *isolate* is a node with no neighbors (that is, with degree
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zero). For directed graphs, this means no in-neighbors and no
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out-neighbors.
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Parameters
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----------
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G : NetworkX graph
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Returns
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-------
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iterator
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An iterator over the isolates of `G`.
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Examples
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--------
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To get a list of all isolates of a graph, use the :class:`list`
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constructor::
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>>> G = nx.Graph()
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>>> G.add_edge(1, 2)
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>>> G.add_node(3)
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>>> list(nx.isolates(G))
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[3]
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To remove all isolates in the graph, first create a list of the
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isolates, then use :meth:`Graph.remove_nodes_from`::
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>>> G.remove_nodes_from(list(nx.isolates(G)))
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>>> list(G)
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[1, 2]
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For digraphs, isolates have zero in-degree and zero out_degre::
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>>> G = nx.DiGraph([(0, 1), (1, 2)])
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>>> G.add_node(3)
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>>> list(nx.isolates(G))
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[3]
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"""
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return (n for n, d in G.degree() if d == 0)
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@nx._dispatchable
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def number_of_isolates(G):
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"""Returns the number of isolates in the graph.
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An *isolate* is a node with no neighbors (that is, with degree
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zero). For directed graphs, this means no in-neighbors and no
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out-neighbors.
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Parameters
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----------
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G : NetworkX graph
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Returns
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-------
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int
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The number of degree zero nodes in the graph `G`.
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"""
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# TODO This can be parallelized.
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return sum(1 for v in isolates(G))
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