support merge two booster

include/LightGBM/boosting.h

@@ -35,6 +35,11 @@ public:
     const ObjectiveFunction* object_function,
     const std::vector<const Metric*>& training_metrics) = 0;
 
+  /*!
+  * \brief Merge model from other boosting object
+  * \param other
+  */
+  virtual void MergeFrom(const Boosting* other) = 0;
   /*!
   * \brief Reset Config for current boosting
   * \param config Configs for boosting
@@ -179,6 +184,7 @@ public:
   Boosting(const Boosting&) = delete;
 
   static void LoadFileToBoosting(Boosting* boosting, const char* filename);
+
   /*!
   * \brief Create boosting object
   * \param type Type of boosting

include/LightGBM/c_api.h

@@ -240,8 +240,18 @@ DllExport int LGBM_BoosterCreateFromModelfile(
 */
 DllExport int LGBM_BoosterFree(BoosterHandle handle);
 
+/*!
+* \brief Merge model in two booster to first handle
+* \param handle handle, will merge other handle to this
+* \param other_handle
+* \return 0 when success, -1 when failure happens
+*/
+DllExport int LGBM_BoosterMerge(BoosterHandle handle,
+  BoosterHandle other_handle);
+
 /*!
 * \brief Add new validation to booster
+* \param handle handle
 * \param valid_data validation data set
 * \return 0 when success, -1 when failure happens
 */
@@ -249,7 +259,8 @@ DllExport int LGBM_BoosterAddValidData(BoosterHandle handle,
   const DatesetHandle valid_data);
 
 /*!
-* \brief Add new validation to booster
+* \brief Reset training data for booster
+* \param handle handle
 * \param train_data training data set
 * \return 0 when success, -1 when failure happens
 */
@@ -258,6 +269,7 @@ DllExport int LGBM_BoosterResetTrainingData(BoosterHandle handle,
 
 /*!
 * \brief Reset config for current booster
+* \param handle handle
 * \param parameters format: 'key1=value1 key2=value2'
 * \return 0 when success, -1 when failure happens
 */
@@ -265,6 +277,7 @@ DllExport int LGBM_BoosterResetParameter(BoosterHandle handle, const char* param
 
 /*!
 * \brief Get number of class 
+* \param handle handle
 * \return number of class
 */
 DllExport int LGBM_BoosterGetNumClasses(BoosterHandle handle, int64_t* out_len);

include/LightGBM/tree.h

@@ -101,10 +101,6 @@ public:
   /*! \brief Serialize this object by string*/
   std::string ToString();
 
-  /*! \brief Disable copy */
-  Tree& operator=(const Tree&) = delete;
-  /*! \brief Disable copy */
-  Tree(const Tree&) = delete;
 private:
   /*!
   * \brief Find leaf index of which record belongs by data

src/boosting/gbdt.h

@@ -36,6 +36,14 @@ public:
                              const std::vector<const Metric*>& training_metrics)
                                                                        override;
 
+  void MergeFrom(const Boosting* other) override {
+    auto other_gbdt = reinterpret_cast<const GBDT*>(other);
+    for (const auto& tree : other_gbdt->models_) {
+      auto new_tree = std::unique_ptr<Tree>(new Tree(*(tree.get())));
+      models_.push_back(std::move(new_tree));
+    }
+  }
+
   /*!
   * \brief Reset Config for current boosting
   * \param config Configs for boosting

src/c_api.cpp

@@ -42,6 +42,10 @@ public:
       Common::ConstPtrInVectorWrapper<Metric>(train_metric_));
   }
 
+  void MergeFrom(const Booster* other) {
+    boosting_->MergeFrom(other->boosting_.get());
+  }
+
   ~Booster() {
 
   }
@@ -465,6 +469,14 @@ DllExport int LGBM_BoosterFree(BoosterHandle handle) {
   API_END();
 }
 
+DllExport int LGBM_BoosterMerge(BoosterHandle handle,
+  BoosterHandle other_handle) {
+  API_BEGIN();
+  Booster* ref_booster = reinterpret_cast<Booster*>(handle);
+  Booster* ref_other_booster = reinterpret_cast<Booster*>(other_handle);
+  ref_booster->MergeFrom(ref_other_booster);
+  API_END();
+}
 
 DllExport int LGBM_BoosterAddValidData(BoosterHandle handle,
   const DatesetHandle valid_data) {