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