Fix bug in sampled distance histogram

src/graph/stats/graph_distance_sampled.hh

@@ -80,14 +80,13 @@ struct get_sampled_distance_histogram
 
         vector<vertex_t> sources;
         sources.reserve(num_vertices(g));
-        int i;
-        for (i = 0; i < int(num_vertices(g)); ++i)
-            if (!is_valid_vertex(vertex(i, g), g))
-                sources.push_back(vertex(i, g));
+        for (auto v : vertices_range(g))
+            sources.push_back(v);
         n_samples = min(n_samples, sources.size());
 
         typename hist_t::point_t point;
         get_vertex_dists_t get_vertex_dists;
+        int i;
         #pragma omp parallel for default(shared) private(i,point) \
             firstprivate(s_hist) schedule(runtime) if (num_vertices(g) * n_samples > 100)
         for (i = 0; i < int(n_samples); ++i)

src/graph_tool/stats/__init__.py

@@ -432,7 +432,7 @@ def distance_histogram(g, weight=None, bins=[0, 1], samples=None,
     [array([   0.,   30.,   88.,  226.,  391.,  240.,   15.]), array([0, 1, 2, 3, 4, 5, 6, 7], dtype=uint...)]
     """
 
-    if samples != None:
+    if samples is not None:
         ret = libgraph_tool_stats.\
               sampled_distance_histogram(g._Graph__graph,
                                          _prop("e", g, weight),