Fixed database typo and removed unnecessary class identifier.

venv/share/doc/networkx-2.5/examples/subclass/plot_antigraph.py

@@ -0,0 +1,191 @@
+"""
+=========
+Antigraph
+=========
+
+Complement graph class for small footprint when working on dense graphs.
+
+This class allows you to add the edges that *do not exist* in the dense
+graph. However, when applying algorithms to this complement graph data
+structure, it behaves as if it were the dense version. So it can be used
+directly in several NetworkX algorithms.
+
+This subclass has only been tested for k-core, connected_components,
+and biconnected_components algorithms but might also work for other
+algorithms.
+
+"""
+import networkx as nx
+from networkx.exception import NetworkXError
+import matplotlib.pyplot as plt
+
+
+class AntiGraph(nx.Graph):
+    """
+    Class for complement graphs.
+
+    The main goal is to be able to work with big and dense graphs with
+    a low memory footprint.
+
+    In this class you add the edges that *do not exist* in the dense graph,
+    the report methods of the class return the neighbors, the edges and
+    the degree as if it was the dense graph. Thus it's possible to use
+    an instance of this class with some of NetworkX functions.
+    """
+
+    all_edge_dict = {"weight": 1}
+
+    def single_edge_dict(self):
+        return self.all_edge_dict
+
+    edge_attr_dict_factory = single_edge_dict
+
+    def __getitem__(self, n):
+        """Return a dict of neighbors of node n in the dense graph.
+
+        Parameters
+        ----------
+        n : node
+           A node in the graph.
+
+        Returns
+        -------
+        adj_dict : dictionary
+           The adjacency dictionary for nodes connected to n.
+
+        """
+        return {
+            node: self.all_edge_dict for node in set(self.adj) - set(self.adj[n]) - {n}
+        }
+
+    def neighbors(self, n):
+        """Return an iterator over all neighbors of node n in the
+           dense graph.
+
+        """
+        try:
+            return iter(set(self.adj) - set(self.adj[n]) - {n})
+        except KeyError as e:
+            raise NetworkXError(f"The node {n} is not in the graph.") from e
+
+    def degree(self, nbunch=None, weight=None):
+        """Return an iterator for (node, degree) in the dense graph.
+
+        The node degree is the number of edges adjacent to the node.
+
+        Parameters
+        ----------
+        nbunch : iterable container, optional (default=all nodes)
+            A container of nodes.  The container will be iterated
+            through once.
+
+        weight : string or None, optional (default=None)
+           The edge attribute that holds the numerical value used
+           as a weight.  If None, then each edge has weight 1.
+           The degree is the sum of the edge weights adjacent to the node.
+
+        Returns
+        -------
+        nd_iter : iterator
+            The iterator returns two-tuples of (node, degree).
+
+        See Also
+        --------
+        degree
+
+        Examples
+        --------
+        >>> G = nx.path_graph(4)  # or DiGraph, MultiGraph, MultiDiGraph, etc
+        >>> list(G.degree(0))  # node 0 with degree 1
+        [(0, 1)]
+        >>> list(G.degree([0, 1]))
+        [(0, 1), (1, 2)]
+
+        """
+        if nbunch is None:
+            nodes_nbrs = (
+                (
+                    n,
+                    {
+                        v: self.all_edge_dict
+                        for v in set(self.adj) - set(self.adj[n]) - {n}
+                    },
+                )
+                for n in self.nodes()
+            )
+        elif nbunch in self:
+            nbrs = set(self.nodes()) - set(self.adj[nbunch]) - {nbunch}
+            return len(nbrs)
+        else:
+            nodes_nbrs = (
+                (
+                    n,
+                    {
+                        v: self.all_edge_dict
+                        for v in set(self.nodes()) - set(self.adj[n]) - {n}
+                    },
+                )
+                for n in self.nbunch_iter(nbunch)
+            )
+
+        if weight is None:
+            return ((n, len(nbrs)) for n, nbrs in nodes_nbrs)
+        else:
+            # AntiGraph is a ThinGraph so all edges have weight 1
+            return (
+                (n, sum((nbrs[nbr].get(weight, 1)) for nbr in nbrs))
+                for n, nbrs in nodes_nbrs
+            )
+
+    def adjacency_iter(self):
+        """Return an iterator of (node, adjacency set) tuples for all nodes
+           in the dense graph.
+
+        This is the fastest way to look at every edge.
+        For directed graphs, only outgoing adjacencies are included.
+
+        Returns
+        -------
+        adj_iter : iterator
+           An iterator of (node, adjacency set) for all nodes in
+           the graph.
+
+        """
+        for n in self.adj:
+            yield (n, set(self.adj) - set(self.adj[n]) - {n})
+
+
+# Build several pairs of graphs, a regular graph
+# and the AntiGraph of it's complement, which behaves
+# as if it were the original graph.
+Gnp = nx.gnp_random_graph(20, 0.8, seed=42)
+Anp = AntiGraph(nx.complement(Gnp))
+Gd = nx.davis_southern_women_graph()
+Ad = AntiGraph(nx.complement(Gd))
+Gk = nx.karate_club_graph()
+Ak = AntiGraph(nx.complement(Gk))
+pairs = [(Gnp, Anp), (Gd, Ad), (Gk, Ak)]
+# test connected components
+for G, A in pairs:
+    gc = [set(c) for c in nx.connected_components(G)]
+    ac = [set(c) for c in nx.connected_components(A)]
+    for comp in ac:
+        assert comp in gc
+# test biconnected components
+for G, A in pairs:
+    gc = [set(c) for c in nx.biconnected_components(G)]
+    ac = [set(c) for c in nx.biconnected_components(A)]
+    for comp in ac:
+        assert comp in gc
+# test degree
+for G, A in pairs:
+    node = list(G.nodes())[0]
+    nodes = list(G.nodes())[1:4]
+    assert G.degree(node) == A.degree(node)
+    assert sum(d for n, d in G.degree()) == sum(d for n, d in A.degree())
+    # AntiGraph is a ThinGraph, so all the weights are 1
+    assert sum(d for n, d in A.degree()) == sum(d for n, d in A.degree(weight="weight"))
+    assert sum(d for n, d in G.degree(nodes)) == sum(d for n, d in A.degree(nodes))
+
+nx.draw(Gnp)
+plt.show()