Implementation of closeness_centrality

docs/source/api.rst

@@ -48,6 +48,7 @@ Centrality
    :toctree: apiref
 
    retworkx.betweenness_centrality
+   retworkx.closeness_centrality
 
 .. _traversal:
 
@@ -289,6 +290,7 @@ the functions from the explicitly typed based on the data type.
    retworkx.digraph_spring_layout
    retworkx.digraph_num_shortest_paths_unweighted
    retworkx.digraph_betweenness_centrality
+   retworkx.digraph_closeness_centrality
    retworkx.digraph_unweighted_average_shortest_path_length
    retworkx.digraph_bfs_search
    retworkx.digraph_dijkstra_search
@@ -336,6 +338,7 @@ typed API based on the data type.
    retworkx.graph_spring_layout
    retworkx.graph_num_shortest_paths_unweighted
    retworkx.graph_betweenness_centrality
+   retworkx.graph_closeness_centrality
    retworkx.graph_unweighted_average_shortest_path_length
    retworkx.graph_bfs_search
    retworkx.graph_dijkstra_search

releasenotes/notes/closeness-centrality-459c5c7e35cb2e63.yaml

@@ -0,0 +1,29 @@
+---
+features:
+  - |
+    Added a new function, :func:`~retworkx.closeness_centrality` to compute
+    closeness centrality of all nodes in a :class:`~retworkx.PyGraph` or
+    :class:`~retworkx.PyDiGraph` object. 
+
+    The closeness centrality of a node :math:`u` is the reciprocal of the
+    average shortest path distance to :math:`u` over all :math:`n-1` reachable
+    nodes.
+
+    .. math::
+
+        C(u) = \frac{n - 1}{\sum_{v=1}^{n-1} d(v, u)},
+
+    where :math:`d(v, u)` is the shortest-path distance between :math:`v` and
+    :math:`u`, and :math:`n` is the number of nodes that can reach :math:`u`.
+
+    Wasserman and Faust propose an improved formula for graphs with more than
+    one connected component. The result is "a ratio of the fraction of actors
+    in the group who are reachable, to the average distance" from the reachable
+    actors.
+
+    .. math::
+
+        C_{WF}(u) = \frac{n-1}{N-1} \frac{n - 1}{\sum_{v=1}^{n-1} d(v, u)},
+
+    where :math:`N` is the number of nodes in the graph. By default, this is
+    enabled.

retworkx-core/src/centrality.rs

@@ -14,14 +14,11 @@ use std::collections::VecDeque;
 use std::sync::RwLock;
 
 use hashbrown::HashMap;
+use petgraph::algo::dijkstra;
 use petgraph::graph::NodeIndex;
 use petgraph::visit::{
-    GraphBase,
-    GraphProp, // allows is_directed
-    IntoNeighborsDirected,
-    IntoNodeIdentifiers,
-    NodeCount,
-    NodeIndexable,
+    GraphBase, GraphProp, IntoEdges, IntoEdgesDirected, IntoNeighborsDirected, IntoNodeIdentifiers,
+    NodeCount, NodeIndexable, Reversed, Visitable,
 };
 use rayon::prelude::*;
 
@@ -297,3 +294,71 @@ where
         sigma,
     }
 }
+
+/// Compute the closeness centrality of all nodes in a graph.
+///
+/// Arguments:
+///
+/// * `graph` - The graph object to run the algorithm on
+/// * `wf_improved` - If True, scale by the fraction of nodes reachable.
+///
+/// # Example
+/// ```rust
+/// use retworkx_core::petgraph;
+/// use retworkx_core::centrality::closeness_centrality;
+///
+/// // Calculate the betweeness centrality of Graph
+/// let g = petgraph::graph::UnGraph::<i32, ()>::from_edges(&[
+///     (0, 4), (1, 2), (2, 3), (3, 4), (1, 4)
+/// ]);
+/// let output = closeness_centrality(&g, true);
+/// assert_eq!(
+///     vec![Some(1./2.), Some(2./3.), Some(4./7.), Some(2./3.), Some(4./5.)],
+///     output
+/// );
+///
+/// // Calculate the betweeness centrality of DiGraph
+/// let dg = petgraph::graph::DiGraph::<i32, ()>::from_edges(&[
+///     (0, 4), (1, 2), (2, 3), (3, 4), (1, 4)
+/// ]);
+/// let output = closeness_centrality(&dg, true);
+/// assert_eq!(
+///     vec![Some(0.), Some(0.), Some(1./4.), Some(1./3.), Some(4./5.)],
+///     output
+/// );
+/// ```
+pub fn closeness_centrality<G>(graph: G, wf_improved: bool) -> Vec<Option<f64>>
+where
+    G: NodeIndexable
+        + IntoNodeIdentifiers
+        + GraphBase
+        + IntoEdges
+        + Visitable
+        + NodeCount
+        + IntoEdgesDirected,
+    G::NodeId: std::hash::Hash + Eq,
+{
+    let max_index = graph.node_bound();
+    let mut betweenness: Vec<Option<f64>> = vec![None; max_index];
+    for node_s in graph.node_identifiers() {
+        let is = graph.to_index(node_s);
+        let map = dijkstra(Reversed(&graph), node_s, None, |_| 1);
+        let mut reachable_nodes_count = 0;
+        let mut dists_sum = 0;
+        for (_, &value) in map.iter() {
+            reachable_nodes_count += 1;
+            dists_sum += value;
+        }
+        if reachable_nodes_count == 1 {
+            betweenness[is] = Some(0.0);
+            continue;
+        }
+        betweenness[is] = Some((reachable_nodes_count - 1) as f64 / dists_sum as f64);
+        if wf_improved {
+            let node_count = graph.node_count();
+            betweenness[is] = betweenness[is]
+                .map(|c| c * (reachable_nodes_count - 1) as f64 / (node_count - 1) as f64);
+        }
+    }
+    betweenness
+}

retworkx-core/tests/centrality.rs

@@ -0,0 +1,124 @@
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations
+// under the License.
+
+use petgraph::visit::Reversed;
+use petgraph::Graph;
+use retworkx_core::centrality::closeness_centrality;
+use retworkx_core::petgraph::graph::{DiGraph, UnGraph};
+
+#[test]
+fn test_simple() {
+    let g = UnGraph::<i32, ()>::from_edges(&[(1, 2), (2, 3), (3, 4), (1, 4)]);
+    let c = closeness_centrality(&g, true);
+    assert_eq!(
+        vec![
+            Some(0.0),
+            Some(0.5625),
+            Some(0.5625),
+            Some(0.5625),
+            Some(0.5625)
+        ],
+        c
+    );
+}
+
+#[test]
+fn test_wf_improved() {
+    let g = UnGraph::<i32, ()>::from_edges(&[(0, 1), (1, 2), (2, 3), (4, 5), (5, 6)]);
+    let c = closeness_centrality(&g, true);
+    assert_eq!(
+        vec![
+            Some(1.0 / 4.0),
+            Some(3.0 / 8.0),
+            Some(3.0 / 8.0),
+            Some(1.0 / 4.0),
+            Some(2.0 / 9.0),
+            Some(1.0 / 3.0),
+            Some(2.0 / 9.0)
+        ],
+        c
+    );
+    let cwf = closeness_centrality(&g, false);
+    assert_eq!(
+        vec![
+            Some(1.0 / 2.0),
+            Some(3.0 / 4.0),
+            Some(3.0 / 4.0),
+            Some(1.0 / 2.0),
+            Some(2.0 / 3.0),
+            Some(1.0),
+            Some(2.0 / 3.0)
+        ],
+        cwf
+    );
+}
+
+#[test]
+fn test_digraph() {
+    let g = DiGraph::<i32, ()>::from_edges(&[(0, 1), (1, 2)]);
+    let c = closeness_centrality(&g, true);
+    assert_eq!(vec![Some(0.), Some(1. / 2.), Some(2. / 3.)], c);
+
+    let cr = closeness_centrality(Reversed(&g), true);
+    assert_eq!(vec![Some(2. / 3.), Some(1. / 2.), Some(0.)], cr);
+}
+
+#[test]
+fn test_k5() {
+    let g = UnGraph::<i32, ()>::from_edges(&[
+        (0, 1),
+        (0, 2),
+        (0, 3),
+        (0, 4),
+        (1, 2),
+        (1, 3),
+        (1, 4),
+        (2, 3),
+        (2, 4),
+        (3, 4),
+    ]);
+    let c = closeness_centrality(&g, true);
+    assert_eq!(
+        vec![Some(1.0), Some(1.0), Some(1.0), Some(1.0), Some(1.0)],
+        c
+    );
+}
+
+#[test]
+fn test_path() {
+    let g = UnGraph::<i32, ()>::from_edges(&[(0, 1), (1, 2)]);
+    let c = closeness_centrality(&g, true);
+    assert_eq!(vec![Some(2.0 / 3.0), Some(1.0), Some(2.0 / 3.0)], c);
+}
+
+#[test]
+fn test_weighted_closeness() {
+    let mut g = Graph::new();
+    let s = g.add_node(0);
+    let u = g.add_node(0);
+    let x = g.add_node(0);
+    let v = g.add_node(0);
+    let y = g.add_node(0);
+    g.add_edge(s, u, 10.);
+    g.add_edge(s, x, 5.);
+    g.add_edge(u, v, 1.);
+    g.add_edge(u, x, 2.);
+    g.add_edge(v, y, 1.);
+    g.add_edge(x, u, 3.);
+    g.add_edge(x, v, 5.);
+    g.add_edge(x, y, 2.);
+    g.add_edge(y, s, 7.);
+    g.add_edge(y, v, 6.);
+    let c = closeness_centrality(&g, true);
+    println!("{:?}", c);
+    assert_eq!(0, 0)
+}

retworkx/__init__.py

@@ -1557,6 +1557,52 @@ def _graph_betweenness_centrality(graph, normalized=True, endpoints=False, paral
     )
 
 
+@functools.singledispatch
+def closeness_centrality(graph, wf_improved=True):
+    r"""Returns the closeness centrality of each node in the graph.
+
+    The closeness centrality of a node :math:`u` is the reciprocal of the
+    average shortest path distance to :math:`u` over all :math:`n-1` reachable
+    nodes.
+
+    .. math::
+
+        C(u) = \frac{n - 1}{\sum_{v=1}^{n-1} d(v, u)},
+
+    where :math:`d(v, u)` is the shortest-path distance between :math:`v` and
+    :math:`u`, and :math:`n` is the number of nodes that can reach :math:`u`.
+
+    Wasserman and Faust propose an improved formula for graphs with more than
+    one connected component. The result is "a ratio of the fraction of actors
+    in the group who are reachable, to the average distance" from the reachable
+    actors.
+
+    .. math::
+
+        C_{WF}(u) = \frac{n-1}{N-1} \frac{n - 1}{\sum_{v=1}^{n-1} d(v, u)},
+
+    where :math:`N` is the number of nodes in the graph.
+
+    :param PyDiGraph graph: The input graph
+    :param bool wf_improved: This is optional; the default is True. If True,
+        scale by the fraction of nodes reachable.
+
+    :returns: A dictionary mapping each node index to its closeness centrality.
+    :rtype: dict
+    """
+    raise TypeError("Invalid input type %s for graph" % type(graph))
+
+
+@closeness_centrality.register(PyDiGraph)
+def _digraph_closeness_centrality(graph, wf_improved=True):
+    return digraph_closeness_centrality(graph, wf_improved=wf_improved)
+
+
+@closeness_centrality.register(PyGraph)
+def _graph_closeness_centrality(graph, wf_improved=True):
+    return graph_closeness_centrality(graph, wf_improved=wf_improved)
+
+
 @functools.singledispatch
 def vf2_mapping(
     first,

src/centrality.rs

@@ -132,3 +132,48 @@ pub fn digraph_betweenness_centrality(
             .collect(),
     }
 }
+
+/// Compute the closeness centrality of all nodes in a PyGraph.
+///
+/// :param PyGraph graph: The input graph
+/// :param bool wf_improved: If True, scale by the fraction of nodes reachable.
+///
+/// :returns: a read-only dict-like object whose keys are the node indices and values are its
+///     closeness centrality score for each node.
+/// :rtype: CentralityMapping
+#[pyfunction(wf_improved = "true")]
+#[pyo3(text_signature = "(graph, /, wf_improved=True)")]
+pub fn graph_closeness_centrality(graph: &graph::PyGraph, wf_improved: bool) -> CentralityMapping {
+    let betweenness = centrality::closeness_centrality(&graph.graph, wf_improved);
+    CentralityMapping {
+        centralities: betweenness
+            .into_iter()
+            .enumerate()
+            .filter_map(|(i, v)| v.map(|x| (i, x)))
+            .collect(),
+    }
+}
+
+/// Compute the closeness centrality of all nodes in a PyDiGraph.
+///
+/// :param PyDiGraph graph: The input digraph
+/// :param bool wf_improved: If True, scale by the fraction of nodes reachable.
+///
+/// :returns: a read-only dict-like object whose keys are the node indices and values are its
+///     closeness centrality score for each node.
+/// :rtype: CentralityMapping
+#[pyfunction(wf_improved = "true")]
+#[pyo3(text_signature = "(graph, /, wf_improved=True)")]
+pub fn digraph_closeness_centrality(
+    graph: &digraph::PyDiGraph,
+    wf_improved: bool,
+) -> CentralityMapping {
+    let betweenness = centrality::closeness_centrality(&graph.graph, wf_improved);
+    CentralityMapping {
+        centralities: betweenness
+            .into_iter()
+            .enumerate()
+            .filter_map(|(i, v)| v.map(|x| (i, x)))
+            .collect(),
+    }
+}

src/lib.rs

@@ -350,6 +350,8 @@ fn retworkx(py: Python<'_>, m: &PyModule) -> PyResult<()> {
     m.add_wrapped(wrap_pyfunction!(graph_all_pairs_dijkstra_shortest_paths))?;
     m.add_wrapped(wrap_pyfunction!(graph_betweenness_centrality))?;
     m.add_wrapped(wrap_pyfunction!(digraph_betweenness_centrality))?;
+    m.add_wrapped(wrap_pyfunction!(graph_closeness_centrality))?;
+    m.add_wrapped(wrap_pyfunction!(digraph_closeness_centrality))?;
     m.add_wrapped(wrap_pyfunction!(graph_astar_shortest_path))?;
     m.add_wrapped(wrap_pyfunction!(digraph_astar_shortest_path))?;
     m.add_wrapped(wrap_pyfunction!(graph_greedy_color))?;