|
|
""" |
|
|
Functions for identifying isolate (degree zero) nodes. |
|
|
""" |
|
|
import networkx as nx |
|
|
|
|
|
__all__ = ["is_isolate", "isolates", "number_of_isolates"] |
|
|
|
|
|
|
|
|
@nx._dispatchable |
|
|
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 |
|
|
|
|
|
|
|
|
@nx._dispatchable |
|
|
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) |
|
|
|
|
|
|
|
|
@nx._dispatchable |
|
|
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`. |
|
|
|
|
|
""" |
|
|
|
|
|
return sum(1 for v in isolates(G)) |
|
|
|
