From a535860067f03f5ece5375fab3c45056db5f035d Mon Sep 17 00:00:00 2001
From: Marc Glisse <marc.glisse@inria.fr>
Date: Fri, 4 Nov 2022 22:39:56 +0100
Subject: New function to insert several vertices in a Simplex_tree

+ tweak insert_graph, in case vertex iteration does not happen in an
increasing order.
---
 src/Simplex_tree/include/gudhi/Simplex_tree.h    | 32 ++++++++++++++++--------
 src/Simplex_tree/test/simplex_tree_unit_test.cpp | 14 +++++++++++
 2 files changed, 36 insertions(+), 10 deletions(-)

diff --git a/src/Simplex_tree/include/gudhi/Simplex_tree.h b/src/Simplex_tree/include/gudhi/Simplex_tree.h
index 9059219c..32168d9e 100644
--- a/src/Simplex_tree/include/gudhi/Simplex_tree.h
+++ b/src/Simplex_tree/include/gudhi/Simplex_tree.h
@@ -24,6 +24,7 @@
 #include <boost/iterator/transform_iterator.hpp>
 #include <boost/graph/adjacency_list.hpp>
 #include <boost/range/adaptor/reversed.hpp>
+#include <boost/range/adaptor/transformed.hpp>
 #include <boost/container/static_vector.hpp>
 
 #ifdef GUDHI_USE_TBB
@@ -1119,16 +1120,12 @@ class Simplex_tree {
       dimension_ = 1;
     }
 
-    root_.members_.reserve(num_vertices(skel_graph));
+    root_.members_.reserve(num_vertices(skel_graph)); // probably useless in most cases
+    auto verts = vertices(skel_graph) | boost::adaptors::transformed([&](auto v){
+        return Dit_value_t(v, Node(&root_, get(vertex_filtration_t(), skel_graph, v))); });
+    root_.members_.insert(boost::begin(verts), boost::end(verts));
+    // This automatically sorts the vertices, the graph concept doesn't guarantee the order in which we iterate.
 
-    typename boost::graph_traits<OneSkeletonGraph>::vertex_iterator v_it,
-        v_it_end;
-    for (std::tie(v_it, v_it_end) = vertices(skel_graph); v_it != v_it_end;
-         ++v_it) {
-      root_.members_.emplace_hint(
-                                  root_.members_.end(), *v_it,
-                                  Node(&root_, get(vertex_filtration_t(), skel_graph, *v_it)));
-    }
     std::pair<typename boost::graph_traits<OneSkeletonGraph>::edge_iterator,
               typename boost::graph_traits<OneSkeletonGraph>::edge_iterator> boost_edges = edges(skel_graph);
     // boost_edges.first is the equivalent to boost_edges.begin()
@@ -1137,7 +1134,7 @@ class Simplex_tree {
       auto edge = *(boost_edges.first);
       auto u = source(edge, skel_graph);
       auto v = target(edge, skel_graph);
-      if (u == v) throw "Self-loops are not simplicial";
+      if (u == v) throw std::invalid_argument("Self-loops are not simplicial");
       // We cannot skip edges with the wrong orientation and expect them to
       // come a second time with the right orientation, that does not always
       // happen in practice. emplace() should be a NOP when an element with the
@@ -1156,6 +1153,21 @@ class Simplex_tree {
     }
   }
 
+  /** \brief Inserts several vertices.
+   * @param[in] vertices A range of Vertex_handle
+   * @param[in] filt filtration value of the new vertices (the same for all)
+   *
+   * This may be faster than inserting the vertices one by one, especially in a random order.
+   * The complex does not need to be empty before calling this function. However, if a vertex is
+   * already present, its filtration value is not modified, unlike with other insertion functions. */
+  template <class VertexRange>
+  void insert_batch_vertices(VertexRange const& vertices, Filtration_value filt = 0) {
+    auto verts = vertices | boost::adaptors::transformed([&](auto v){
+        return Dit_value_t(v, Node(&root_, filt)); });
+    root_.members_.insert(boost::begin(verts), boost::end(verts));
+    if (dimension_ < 0 && !root_.members_.empty()) dimension_ = 0;
+  }
+
   /** \brief Expands the Simplex_tree containing only its one skeleton
    * until dimension max_dim.
    *
diff --git a/src/Simplex_tree/test/simplex_tree_unit_test.cpp b/src/Simplex_tree/test/simplex_tree_unit_test.cpp
index 79bb5a93..ebcc406c 100644
--- a/src/Simplex_tree/test/simplex_tree_unit_test.cpp
+++ b/src/Simplex_tree/test/simplex_tree_unit_test.cpp
@@ -1038,3 +1038,17 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(simplex_tree_boundaries_and_opposite_vertex_iterat
       BOOST_CHECK(opposite_vertices.size() == 0);
   }
 }
+
+BOOST_AUTO_TEST_CASE(batch_vertices) {
+  typedef Simplex_tree<> typeST;
+  std::clog << "********************************************************************" << std::endl;
+  std::clog << "TEST BATCH VERTEX INSERTION" << std::endl;
+  typeST st;
+  st.insert_simplex_and_subfaces({3}, 1.5);
+  std::vector verts { 2, 3, 5, 6 };
+  st.insert_batch_vertices(verts);
+  BOOST_CHECK(st.num_vertices() == 4);
+  BOOST_CHECK(st.num_simplices() == 4);
+  BOOST_CHECK(st.filtration(st.find({2})) == 0.);
+  BOOST_CHECK(st.filtration(st.find({3})) == 1.5);
+}
-- 
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