Faster version of convertFrom when no label translation needed

gtsam/discrete/DecisionTree-inl.h

@@ -557,9 +557,7 @@ namespace gtsam {
   template <typename X, typename Func>
   DecisionTree<L, Y>::DecisionTree(const DecisionTree<L, X>& other,
                                    Func Y_of_X) {
-    // Define functor for identity mapping of node label.
+    root_ = convertFrom<X>(other.root_, Y_of_X);
-    auto L_of_L = [](const L& label) { return label; };
-    root_ = convertFrom<L, X>(other.root_, L_of_L, Y_of_X);
   }
 
   /****************************************************************************/
@@ -698,6 +696,36 @@ namespace gtsam {
     }
   }
 
+  /****************************************************************************/
+  template <typename L, typename Y>
+  template <typename X>
+  typename DecisionTree<L, Y>::NodePtr DecisionTree<L, Y>::convertFrom(
+      const typename DecisionTree<L, X>::NodePtr& f,
+      std::function<Y(const X&)> Y_of_X) {
+
+    // If leaf, apply unary conversion "op" and create a unique leaf.
+    using LXLeaf = typename DecisionTree<L, X>::Leaf;
+    if (auto leaf = std::dynamic_pointer_cast<const LXLeaf>(f)) {
+      return NodePtr(new Leaf(Y_of_X(leaf->constant())));
+    }
+
+    // Check if Choice
+    using LXChoice = typename DecisionTree<L, X>::Choice;
+    auto choice = std::dynamic_pointer_cast<const LXChoice>(f);
+    if (!choice) throw std::invalid_argument(
+        "DecisionTree::convertFrom: Invalid NodePtr");
+
+    // Create a new Choice node with the same label
+    auto newChoice = std::make_shared<Choice>(choice->label(), choice->nrChoices());
+
+    // Convert each branch recursively
+    for (auto&& branch : choice->branches()) {
+      newChoice->push_back(convertFrom<X>(branch, Y_of_X));
+    }
+
+    return Choice::Unique(newChoice);
+  }
+
   /****************************************************************************/
   template <typename L, typename Y>
   template <typename M, typename X>
@@ -745,8 +773,9 @@ namespace gtsam {
    *
    * NOTE: We differentiate between leaves and assignments. Concretely, a 3
    * binary variable tree will have 2^3=8 assignments, but based on pruning, it
-   * can have <8 leaves. For example, if a tree has all assignment values as 1,
+   * can have less than 8 leaves. For example, if a tree has all assignment
-   * then pruning will cause the tree to have only 1 leaf yet 8 assignments.
+   * values as 1, then pruning will cause the tree to have only 1 leaf yet 8
+   * assignments.
    */
   template <typename L, typename Y>
   struct Visit {

gtsam/discrete/DecisionTree.h

@@ -165,6 +165,19 @@ namespace gtsam {
     template <typename It, typename ValueIt>
     NodePtr create(It begin, It end, ValueIt beginY, ValueIt endY) const;
 
+    /**
+     * @brief Convert from a DecisionTree<L, X> to DecisionTree<L, Y>.
+     *
+     * @tparam M The previous label type.
+     * @tparam X The previous value type.
+     * @param f The node pointer to the root of the previous DecisionTree.
+     * @param Y_of_X Functor to convert from value type X to type Y.
+     * @return NodePtr
+     */
+    template <typename X>
+    static NodePtr convertFrom(const typename DecisionTree<L, X>::NodePtr& f,
+                               std::function<Y(const X&)> Y_of_X);
+
     /**
      * @brief Convert from a DecisionTree<M, X> to DecisionTree<L, Y>.
      *