"""Operations on many graphs.
"""
from itertools import zip_longest
import networkx as nx
__all__ = ["union_all", "compose_all", "disjoint_union_all", "intersection_all"]
[docs]def union_all(graphs, rename=(None,)):
"""Returns the union of all graphs.
The graphs must be disjoint, otherwise an exception is raised.
Parameters
----------
graphs : list of graphs
List of NetworkX graphs
rename : bool , default=(None, None)
Node names of G and H can be changed by specifying the tuple
rename=('G-','H-') (for example). Node "u" in G is then renamed
"G-u" and "v" in H is renamed "H-v".
Returns
-------
U : a graph with the same type as the first graph in list
Raises
------
ValueError
If `graphs` is an empty list.
Notes
-----
To force a disjoint union with node relabeling, use
disjoint_union_all(G,H) or convert_node_labels_to integers().
Graph, edge, and node attributes are propagated to the union graph.
If a graph attribute is present in multiple graphs, then the value
from the last graph in the list with that attribute is used.
See Also
--------
union
disjoint_union_all
"""
if not graphs:
raise ValueError("cannot apply union_all to an empty list")
graphs_names = zip_longest(graphs, rename)
U, gname = next(graphs_names)
for H, hname in graphs_names:
U = nx.union(U, H, (gname, hname))
gname = None
return U
[docs]def disjoint_union_all(graphs):
"""Returns the disjoint union of all graphs.
This operation forces distinct integer node labels starting with 0
for the first graph in the list and numbering consecutively.
Parameters
----------
graphs : list
List of NetworkX graphs
Returns
-------
U : A graph with the same type as the first graph in list
Raises
------
ValueError
If `graphs` is an empty list.
Notes
-----
It is recommended that the graphs be either all directed or all undirected.
Graph, edge, and node attributes are propagated to the union graph.
If a graph attribute is present in multiple graphs, then the value
from the last graph in the list with that attribute is used.
"""
if not graphs:
raise ValueError("cannot apply disjoint_union_all to an empty list")
graphs = iter(graphs)
U = next(graphs)
for H in graphs:
U = nx.disjoint_union(U, H)
return U
[docs]def compose_all(graphs):
"""Returns the composition of all graphs.
Composition is the simple union of the node sets and edge sets.
The node sets of the supplied graphs need not be disjoint.
Parameters
----------
graphs : list
List of NetworkX graphs
Returns
-------
C : A graph with the same type as the first graph in list
Raises
------
ValueError
If `graphs` is an empty list.
Notes
-----
It is recommended that the supplied graphs be either all directed or all
undirected.
Graph, edge, and node attributes are propagated to the union graph.
If a graph attribute is present in multiple graphs, then the value
from the last graph in the list with that attribute is used.
"""
if not graphs:
raise ValueError("cannot apply compose_all to an empty list")
graphs = iter(graphs)
C = next(graphs)
for H in graphs:
C = nx.compose(C, H)
return C
[docs]def intersection_all(graphs):
"""Returns a new graph that contains only the edges that exist in
all graphs.
All supplied graphs must have the same node set.
Parameters
----------
graphs : list
List of NetworkX graphs
Returns
-------
R : A new graph with the same type as the first graph in list
Raises
------
ValueError
If `graphs` is an empty list.
Notes
-----
Attributes from the graph, nodes, and edges are not copied to the new
graph.
"""
if not graphs:
raise ValueError("cannot apply intersection_all to an empty list")
graphs = iter(graphs)
R = next(graphs)
for H in graphs:
R = nx.intersection(R, H)
return R