added random to ranges

src/polymesh/impl/impl_ranges.hh

@@ -448,6 +448,23 @@ iterator smart_collection<mesh_ptr, tag, iterator>::end() const
     return {{this->mesh, typename primitive<tag>::index(primitive<tag>::all_size(*this->mesh))}};
 }
 
+template <class mesh_ptr, class tag, class iterator>
+template <class Generator>
+typename primitive<tag>::handle smart_collection<mesh_ptr, tag, iterator>::random(Generator &g) const
+{
+    auto s = primitive<tag>::all_size(*this->mesh);
+    assert(s > 0 && "Cannot chose from empty mesh");
+    std::uniform_int_distribution<> uniform(0, s - 1);
+
+    typename primitive<tag>::handle h = {this->mesh, typename primitive<tag>::index(uniform(g))};
+
+    if (iterator::is_valid_iterator)
+        while (h.is_removed())
+            h = {this->mesh, typename primitive<tag>::index(uniform(g))};
+
+    return h;
+}
+
 template <class iterator>
 void vertex_collection<iterator>::remove(vertex_handle v) const
 {

src/polymesh/iterators.hh

@@ -16,6 +16,9 @@ struct valid_primitive_iterator
 {
     using handle_t = typename primitive<tag>::handle;
 
+    static const bool is_all_iterator = false;
+    static const bool is_valid_iterator = true;
+
     valid_primitive_iterator() = default;
     valid_primitive_iterator(handle_t handle) : handle(handle) { this->handle.idx = handle.mesh->next_valid_idx_from(handle.idx); }
 
@@ -53,6 +56,9 @@ struct all_primitive_iterator
 {
     using handle_t = typename primitive<tag>::handle;
 
+    static const bool is_all_iterator = true;
+    static const bool is_valid_iterator = false;
+
     all_primitive_iterator() = default;
     all_primitive_iterator(handle_t handle) : handle(handle) {}
 

src/polymesh/ranges.hh

@@ -175,6 +175,12 @@ struct smart_collection : smart_range<smart_collection<mesh_ptr, tag, iterator>,
     iterator begin() const;
     iterator end() const;
 
+    /// returns a handle chosen uniformly at random
+    /// NOTE: when only valid handles are allowed, this will use rejection sampling
+    ///       and thus get very slow if a lot of data is invalid
+    template <class Generator>
+    handle random(Generator& g) const;
+
 protected:
     /// Backreference to mesh
     mesh_ptr mesh;