Implement label_largest_component() and return label histogram in label_components()

src/graph/topology/graph_components.cc

@@ -20,29 +20,34 @@
 
 #include "graph_components.hh"
 
+#include "numpy_bind.hh"
+
 #include <boost/python.hpp>
 
 using namespace std;
 using namespace boost;
 using namespace graph_tool;
 
-void  do_label_components(GraphInterface& gi, boost::any prop)
+python::object do_label_components(GraphInterface& gi, boost::any prop)
 {
-    run_action<>()(gi, label_components(),
+    vector<size_t> hist;
+    run_action<>()(gi, bind<void>(label_components(), _1, _2, ref(hist)),
                    writable_vertex_scalar_properties())(prop);
+    return wrap_vector_owned(hist);
 }
 
-size_t do_label_biconnected_components(GraphInterface& gi, boost::any comp,
+python::object
+do_label_biconnected_components(GraphInterface& gi, boost::any comp,
                                 boost::any art)
 {
-    size_t nc;
+    vector<size_t> hist;
     run_action<graph_tool::detail::never_directed>()
         (gi, bind<void>(label_biconnected_components(), _1, _2, _3,
-                        ref(nc)),
+                        ref(hist)),
          writable_edge_scalar_properties(),
          writable_vertex_scalar_properties())
         (comp, art);
-    return nc;
+    return wrap_vector_owned(hist);
 }
 
 void export_components()

src/graph/topology/graph_components.hh

@@ -20,22 +20,93 @@
 #include <boost/graph/strong_components.hpp>
 #include <boost/graph/biconnected_components.hpp>
 
+namespace graph_tool
+{
+template <class PropertyMap>
+class HistogramPropertyMap;
+}
+
+namespace boost
+{
+template <class PropertyMap>
+struct property_traits<HistogramPropertyMap<PropertyMap> >:
+        public property_traits<PropertyMap> {};
+}
+
 namespace graph_tool
 {
 using namespace std;
 using namespace boost;
 
+// this wraps an existing property map, and makes a simple histogram of the
+// values (assumed to be an integer type)
+
+template <class PropertyMap>
+class HistogramPropertyMap
+{
+public:
+    typedef typename property_traits<PropertyMap>::value_type value_type;
+    typedef typename property_traits<PropertyMap>::key_type key_type;
+    typedef typename property_traits<PropertyMap>::category category;
+
+    HistogramPropertyMap(PropertyMap base_map, size_t max, vector<size_t>& hist)
+        : _base_map(base_map), _max(max), _hist(hist) {}
+    HistogramPropertyMap(){}
+
+    value_type get(const key_type& k) const
+    {
+        return boost::get(_base_map, k);
+    }
+
+    void put(const key_type& k, const value_type& v)
+    {
+        boost::put(_base_map, k, v);
+
+        vector<size_t>& h = _hist;
+        size_t bin = v;        
+        if (bin > _max)
+            return;
+        if (bin >= h.size())
+            h.resize(bin + 1);
+        ++h[bin];
+    }
+
+private:
+    PropertyMap _base_map;
+    size_t _max;
+    boost::reference_wrapper<vector<size_t> > _hist;
+};
+
+template <class PropertyMap>
+typename property_traits<PropertyMap>::value_type
+get(const HistogramPropertyMap<PropertyMap>& pmap,
+    const typename property_traits<PropertyMap>::key_type& k)
+{
+    return pmap.get(k);
+}
+
+template <class PropertyMap>
+void put(HistogramPropertyMap<PropertyMap> pmap,
+         const typename property_traits<PropertyMap>::key_type& k,
+         const typename property_traits<PropertyMap>::value_type& val)
+{
+    pmap.put(k, val);
+}
+
+
 // this will label the components of a graph to a given vertex property, from
-// [0, number of components - 1]. If the graph is directed the strong
-// components are used.
+// [0, number of components - 1], and keep an histogram. If the graph is
+// directed the strong components are used.
 struct label_components
 {
     template <class Graph, class CompMap>
-    void operator()(const Graph& g, CompMap comp_map) const
+    void operator()(const Graph& g, CompMap comp_map, vector<size_t>& hist)
+        const
     {
         typedef typename graph_traits<Graph>::directed_category
             directed_category;
-        get_components(g, comp_map,
+        HistogramPropertyMap<CompMap> cm(comp_map, num_vertices(g), hist);
+        get_components(g, cm,
                        typename is_convertible<directed_category,
                                                directed_tag>::type());
     }
@@ -80,9 +151,10 @@ struct label_biconnected_components
 
     template <class Graph, class CompMap, class ArtMap>
     void operator()(const Graph& g, CompMap comp_map, ArtMap art_map,
-                    size_t& nc) const
+                    vector<size_t>& hist) const
     {
-        nc = biconnected_components(g, comp_map,
+        HistogramPropertyMap<CompMap> cm(comp_map, num_edges(g), hist);
+        biconnected_components(g, cm,
                                vertex_inserter<ArtMap>(art_map)).first;
     }
 };

src/graph_tool/topology/__init__.py

@@ -50,11 +50,11 @@ from .. dl_import import dl_import
 dl_import("import libgraph_tool_topology")
 
 from .. import _prop, Vector_int32_t, _check_prop_writable, \
-     _check_prop_scalar,  _check_prop_vector, Graph, PropertyMap
+     _check_prop_scalar, _check_prop_vector, Graph, PropertyMap, GraphView
 import random, sys, numpy, weakref
 __all__ = ["isomorphism", "subgraph_isomorphism", "mark_subgraph",
            "min_spanning_tree", "dominator_tree", "topological_sort",
-           "transitive_closure", "label_components",
+           "transitive_closure", "label_components", "label_largest_component",
            "label_biconnected_components", "shortest_distance",
            "shortest_path", "is_planar"]
 
@@ -422,15 +422,16 @@ def label_components(g, vprop=None, directed=None):
     Label the components to which each vertex in the graph belongs. If the
     graph is directed, it finds the strongly connected components.
 
+    A property map with the component labels is returned, together with an
+    histogram of component labels.
+
     Parameters
     ----------
     g : :class:`~graph_tool.Graph`
         Graph to be used.
-
     vprop : :class:`~graph_tool.PropertyMap` (optional, default: None)
         Vertex property to store the component labels. If none is supplied, one
         is created.
-
     directed : bool (optional, default:None)
         Treat graph as directed or not, independently of its actual
         directionality.
@@ -439,6 +440,8 @@ def label_components(g, vprop=None, directed=None):
     -------
     comp : :class:`~graph_tool.PropertyMap`
         Vertex property map with component labels.
+    hist : :class:`~numpy.ndarray`
+        Histogram of component labels.
 
     Notes
     -----
@@ -452,11 +455,13 @@ def label_components(g, vprop=None, directed=None):
     >>> from numpy.random import seed
     >>> seed(43)
     >>> g = gt.random_graph(100, lambda: (1, 1))
-    >>> comp = gt.label_components(g)
+    >>> comp, hist = gt.label_components(g)
     >>> print comp.get_array()
     [0 0 1 0 0 0 1 0 0 0 0 0 1 0 0 2 0 0 0 1 0 0 0 0 1 1 0 2 0 1 1 0 0 0 0 1 0
      0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 2 0 0 0 0 1 0 0 0 0 0 1 0 0 0
      1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0]
+    >>> print hist
+    [81 15  4]
     """
 
     if vprop is None:
@@ -465,17 +470,57 @@ def label_components(g, vprop=None, directed=None):
     _check_prop_writable(vprop, name="vprop")
     _check_prop_scalar(vprop, name="vprop")
 
-    try:
     if directed is not None:
-            g.stash_filter(directed=True)
-            g.set_directed(directed)
+        g = GraphView(g, directed=directed)
 
-        libgraph_tool_topology.\
+    hist = libgraph_tool_topology.\
                label_components(g._Graph__graph, _prop("v", g, vprop))
-    finally:
-        if directed is not None:
-            g.pop_filter(directed=True)
-    return vprop
+    return vprop, hist
+
+
+def label_largest_component(g, directed=None):
+    """
+    Label the largest component in the graph. If the graph is directed, it
+    labels the largest strongly connected components.
+
+    A property map with a boolean label is returned.
+
+    Parameters
+    ----------
+    g : :class:`~graph_tool.Graph`
+        Graph to be used.
+    directed : bool (optional, default:None)
+        Treat graph as directed or not, independently of its actual
+        directionality.
+
+    Returns
+    -------
+    comp : :class:`~graph_tool.PropertyMap`
+        Vertex property map which labels the largest component with value 1.
+
+    Notes
+    -----
+    The algorithm runs in :math:`O(V + E)` time.
+
+    Examples
+    --------
+    >>> from numpy.random import seed, poisson
+    >>> seed(43)
+    >>> g = gt.random_graph(100, lambda: poisson(1), directed=False)
+    >>> l = gt.label_largest_component(g)
+    >>> print l.a
+    [1 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0
+     0 0 1 1 0 0 1 0 0 1 0 0 0 1 1 0 0 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 1
+     0 0 0 0 1 0 0 1 0 1 1 0 1 1 0 0 0 0 0 0 1 1 0 0 0 0]
+    >>> u = gt.GraphView(g, vfilt=l)   # extract the largest component as a graph
+    >>> print u.num_vertices()
+    26
+    """
+
+    label = g.new_vertex_property("bool")
+    c, h = label_components(g, directed=directed)
+    label.a = c.a == h.argmax()
+    return label
 
 
 def label_biconnected_components(g, eprop=None, vprop=None):
@@ -483,6 +528,10 @@ def label_biconnected_components(g, eprop=None, vprop=None):
     Label the edges of biconnected components, and the vertices which are
     articulation points.
 
+    An edge property map with the component labels is returned, together a
+    boolean vertex map marking the articulation points, and an histogram of
+    component labels.
+
     Parameters
     ----------
     g : :class:`~graph_tool.Graph`
@@ -529,7 +578,7 @@ def label_biconnected_components(g, eprop=None, vprop=None):
     >>> from numpy.random import seed
     >>> seed(43)
     >>> g = gt.random_graph(100, lambda: 2, directed=False)
-    >>> comp, art, nc = gt.label_biconnected_components(g)
+    >>> comp, art, hist = gt.label_biconnected_components(g)
     >>> print comp.a
     [1 0 0 0 2 0 1 0 0 0 0 0 1 0 0 3 0 0 0 0 0 0 0 0 2 0 0 0 0 0 1 1 0 0 0 0 0
      1 0 1 3 0 2 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 3 0 0 0 0 0 0 0 0 0 1 0
@@ -538,8 +587,8 @@ def label_biconnected_components(g, eprop=None, vprop=None):
     [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
      0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
      0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
-    >>> print nc
-    4
+    >>> print hist
+    [77 13  6  4]
 
     """
 
@@ -553,15 +602,11 @@ def label_biconnected_components(g, eprop=None, vprop=None):
     _check_prop_writable(eprop, name="eprop")
     _check_prop_scalar(eprop, name="eprop")
 
-    g.stash_filter(directed=True)
-    try:
-        g.set_directed(False)
-        nc = libgraph_tool_topology.\
+    g = GraphView(g, directed=False)
+    hist = libgraph_tool_topology.\
              label_biconnected_components(g._Graph__graph, _prop("e", g, eprop),
                                           _prop("v", g, vprop))
-    finally:
-        g.pop_filter(directed=True)
-    return eprop, vprop, nc
+    return eprop, vprop, hist
 
 
 def shortest_distance(g, source=None, weights=None, max_dist=None,