add get/set c_api for leaf value

include/LightGBM/c_api.h

@@ -499,6 +499,32 @@ DllExport int LGBM_BoosterDumpModel(BoosterHandle handle,
   int64_t* out_len,
   char** out_str);
 
+/*!
+* \brief Get leaf value 
+* \param handle handle
+* \param tree_idx index of tree
+* \param leaf_idx index of leaf
+* \param out_val out result
+* \return 0 when succeed, -1 when failure happens
+*/
+DllExport int LGBM_BoosterGetLeafValue(BoosterHandle handle,
+  int tree_idx,
+  int leaf_idx,
+  float* out_val);
+
+/*!
+* \brief Set leaf value
+* \param handle handle
+* \param tree_idx index of tree
+* \param leaf_idx index of leaf
+* \param val leaf value
+* \return 0 when succeed, -1 when failure happens
+*/
+DllExport int LGBM_BoosterSetLeafValue(BoosterHandle handle,
+  int tree_idx,
+  int leaf_idx,
+  float val);
+
 // some help functions used to convert data
 
 std::function<std::vector<double>(int row_idx)>

include/LightGBM/tree.h

@@ -50,9 +50,14 @@ public:
     double threshold_double, double left_value,
     double right_value, data_size_t left_cnt, data_size_t right_cnt, double gain);
 
-  /*! \brief Get the output of one leave */
+  /*! \brief Get the output of one leaf */
   inline double LeafOutput(int leaf) const { return leaf_value_[leaf]; }
 
+  /*! \brief Set the output of one leaf */
+  inline void SetLeafOutput(int leaf, double output) {
+    leaf_value_[leaf] = output;
+  }
+
   /*!
   * \brief Adding prediction value of this tree model to scores
   * \param data The dataset

src/boosting/gbdt.h

@@ -193,6 +193,18 @@ public:
       static_cast<int>(models_.size()) / num_class_);
   }
 
+  inline double GetLeafValue(int tree_idx, int leaf_idx) const {
+    CHECK(tree_idx >= 0 && static_cast<size_t>(tree_idx) < models_.size());
+    CHECK(leaf_idx >= 0 && leaf_idx < models_[tree_idx]->num_leaves());
+    return models_[tree_idx]->LeafOutput(leaf_idx);
+  }
+
+  inline void SetLeafValue(int tree_idx, int leaf_idx, double val) {
+    CHECK(tree_idx >= 0 && static_cast<size_t>(tree_idx) < models_.size());
+    CHECK(leaf_idx >= 0 && leaf_idx < models_[tree_idx]->num_leaves());
+    models_[tree_idx]->SetLeafOutput(leaf_idx, val);
+  }
+
   /*!
   * \brief Get Type name of this boosting object
   */

src/c_api.cpp

@@ -19,6 +19,7 @@
 #include <mutex>
 
 #include "./application/predictor.hpp"
+#include "./boosting/gbdt.h"
 
 namespace LightGBM {
 
@@ -190,6 +191,15 @@ public:
     return boosting_->DumpModel();
   }
 
+  double GetLeafValue(int tree_idx, int leaf_idx) const {
+    return dynamic_cast<GBDT*>(boosting_.get())->GetLeafValue(tree_idx, leaf_idx);
+  }
+
+  void SetLeafValue(int tree_idx, int leaf_idx, double val) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    dynamic_cast<GBDT*>(boosting_.get())->SetLeafValue(tree_idx, leaf_idx, val);
+  }
+
   int GetEvalCounts() const {
     int ret = 0;
     for (const auto& metric : train_metric_) {
@@ -788,6 +798,29 @@ DllExport int LGBM_BoosterDumpModel(BoosterHandle handle,
   API_END();
 }
 
+
+
+DllExport int LGBM_BoosterGetLeafValue(BoosterHandle handle,
+  int tree_idx,
+  int leaf_idx,
+  float* out_val) {
+  API_BEGIN();
+  Booster* ref_booster = reinterpret_cast<Booster*>(handle);
+  *out_val = static_cast<float>(ref_booster->GetLeafValue(tree_idx, leaf_idx));
+  API_END();
+}
+
+
+DllExport int LGBM_BoosterSetLeafValue(BoosterHandle handle,
+  int tree_idx,
+  int leaf_idx,
+  float val) {
+  API_BEGIN();
+  Booster* ref_booster = reinterpret_cast<Booster*>(handle);
+  ref_booster->SetLeafValue(tree_idx, leaf_idx, static_cast<double>(val));
+  API_END();
+}
+
 // ---- start of some help functions
 
 std::function<std::vector<double>(int row_idx)>