compose#

compose(G, H)[source]#

Returns a new graph of G composed with H.

Composition is the simple union of the node sets and edge sets. The node sets of G and H do not need to be disjoint.

Parameters
G, Hgraph

A NetworkX graph

Returns
C: A new graph with the same type as G

Notes

It is recommended that G and H be either both directed or both undirected. Attributes from H take precedent over attributes from G.

For MultiGraphs, the edges are identified by incident nodes AND edge-key. This can cause surprises (i.e., edge (1, 2) may or may not be the same in two graphs) if you use MultiGraph without keeping track of edge keys.

Examples

>>> G = nx.Graph([(0, 1), (0, 2)])
>>> H = nx.Graph([(0, 1), (1, 2)])
>>> R = nx.compose(G, H)
>>> R.nodes
NodeView((0, 1, 2))
>>> R.edges
EdgeView([(0, 1), (0, 2), (1, 2)])

By default, the attributes from H take precedent over attributes from G. If you prefer another way of combining attributes, you can update them after the compose operation:

>>> G = nx.Graph([(0, 1, {'weight': 2.0}), (3, 0, {'weight': 100.0})])
>>> H = nx.Graph([(0, 1, {'weight': 10.0}), (1, 2, {'weight': -1.0})])
>>> nx.set_node_attributes(G, {0: 'dark', 1: 'light', 3: 'black'}, name='color')
>>> nx.set_node_attributes(H, {0: 'green', 1: 'orange', 2: 'yellow'}, name='color')
>>> GcomposeH = nx.compose(G, H)

Normally, color attribute values of nodes of GcomposeH come from H. We can workaround this as follows:

>>> node_data = {n: G.nodes[n]['color'] + " " + H.nodes[n]['color'] for n in G.nodes & H.nodes}
>>> nx.set_node_attributes(GcomposeH, node_data, 'color')
>>> print(GcomposeH.nodes[0]['color'])
dark green

>>> print(GcomposeH.nodes[3]['color'])
black

Similarly, we can update edge attributes after the compose operation in a way we prefer:

>>> edge_data = {e: G.edges[e]['weight'] * H.edges[e]['weight'] for e in G.edges & H.edges}
>>> nx.set_edge_attributes(GcomposeH, edge_data, 'weight')
>>> print(GcomposeH.edges[(0, 1)]['weight'])
20.0

>>> print(GcomposeH.edges[(3, 0)]['weight'])
100.0