Fixed database typo and removed unnecessary class identifier.

venv/Lib/site-packages/networkx/algorithms/bipartite/redundancy.py

@@ -0,0 +1,111 @@
+"""Node redundancy for bipartite graphs."""
+from itertools import combinations
+
+from networkx import NetworkXError
+
+__all__ = ["node_redundancy"]
+
+
+def node_redundancy(G, nodes=None):
+    r"""Computes the node redundancy coefficients for the nodes in the bipartite
+    graph `G`.
+
+    The redundancy coefficient of a node `v` is the fraction of pairs of
+    neighbors of `v` that are both linked to other nodes. In a one-mode
+    projection these nodes would be linked together even if `v` were
+    not there.
+
+    More formally, for any vertex `v`, the *redundancy coefficient of `v`* is
+    defined by
+
+    .. math::
+
+        rc(v) = \frac{|\{\{u, w\} \subseteq N(v),
+        \: \exists v' \neq  v,\: (v',u) \in E\:
+        \mathrm{and}\: (v',w) \in E\}|}{ \frac{|N(v)|(|N(v)|-1)}{2}},
+
+    where `N(v)` is the set of neighbors of `v` in `G`.
+
+    Parameters
+    ----------
+    G : graph
+        A bipartite graph
+
+    nodes : list or iterable (optional)
+        Compute redundancy for these nodes. The default is all nodes in G.
+
+    Returns
+    -------
+    redundancy : dictionary
+        A dictionary keyed by node with the node redundancy value.
+
+    Examples
+    --------
+    Compute the redundancy coefficient of each node in a graph::
+
+        >>> from networkx.algorithms import bipartite
+        >>> G = nx.cycle_graph(4)
+        >>> rc = bipartite.node_redundancy(G)
+        >>> rc[0]
+        1.0
+
+    Compute the average redundancy for the graph::
+
+        >>> from networkx.algorithms import bipartite
+        >>> G = nx.cycle_graph(4)
+        >>> rc = bipartite.node_redundancy(G)
+        >>> sum(rc.values()) / len(G)
+        1.0
+
+    Compute the average redundancy for a set of nodes::
+
+        >>> from networkx.algorithms import bipartite
+        >>> G = nx.cycle_graph(4)
+        >>> rc = bipartite.node_redundancy(G)
+        >>> nodes = [0, 2]
+        >>> sum(rc[n] for n in nodes) / len(nodes)
+        1.0
+
+    Raises
+    ------
+    NetworkXError
+        If any of the nodes in the graph (or in `nodes`, if specified) has
+        (out-)degree less than two (which would result in division by zero,
+        according to the definition of the redundancy coefficient).
+
+    References
+    ----------
+    .. [1] Latapy, Matthieu, Clémence Magnien, and Nathalie Del Vecchio (2008).
+       Basic notions for the analysis of large two-mode networks.
+       Social Networks 30(1), 31--48.
+
+    """
+    if nodes is None:
+        nodes = G
+    if any(len(G[v]) < 2 for v in nodes):
+        raise NetworkXError(
+            "Cannot compute redundancy coefficient for a node"
+            " that has fewer than two neighbors."
+        )
+    # TODO This can be trivially parallelized.
+    return {v: _node_redundancy(G, v) for v in nodes}
+
+
+def _node_redundancy(G, v):
+    """Returns the redundancy of the node `v` in the bipartite graph `G`.
+
+    If `G` is a graph with `n` nodes, the redundancy of a node is the ratio
+    of the "overlap" of `v` to the maximum possible overlap of `v`
+    according to its degree. The overlap of `v` is the number of pairs of
+    neighbors that have mutual neighbors themselves, other than `v`.
+
+    `v` must have at least two neighbors in `G`.
+
+    """
+    n = len(G[v])
+    # TODO On Python 3, we could just use `G[u].keys() & G[w].keys()` instead
+    # of instantiating the entire sets.
+    overlap = sum(
+        1 for (u, w) in combinations(G[v], 2) if (set(G[u]) & set(G[w])) - {v}
+    )
+    return (2 * overlap) / (n * (n - 1))