contracted_edge¶

contracted_edge
(G, edge, self_loops=True)[source]¶ Returns the graph that results from contracting the specified edge.
Edge contraction identifies the two endpoints of the edge as a single node incident to any edge that was incident to the original two nodes. A graph that results from edge contraction is called a minor of the original graph.
Parameters:  G (NetworkX graph) – The graph whose edge will be contracted.
 edge (tuple) – Must be a pair of nodes in
G
.  self_loops (Boolean) – If this is
True
, any edges (includingedge
) joining the endpoints ofedge
inG
become selfloops on the new node in the returned graph.
Returns: A new graph object of the same type as
G
(leavingG
unmodified) with endpoints ofedge
identified in a single node. The right node ofedge
will be merged into the left one, so only the left one will appear in the returned graph.Return type: Networkx graph
Raises: ValueError
– Ifedge
is not an edge inG
.Examples
Attempting to contract two nonadjacent nodes yields an error:
>>> import networkx as nx >>> G = nx.cycle_graph(4) >>> nx.contracted_edge(G, (1, 3)) Traceback (most recent call last): ... ValueError: Edge (1, 3) does not exist in graph G; cannot contract it
Contracting two adjacent nodes in the cycle graph on n nodes yields the cycle graph on n  1 nodes:
>>> import networkx as nx >>> C5 = nx.cycle_graph(5) >>> C4 = nx.cycle_graph(4) >>> M = nx.contracted_edge(C5, (0, 1), self_loops=False) >>> nx.is_isomorphic(M, C4) True
See also