add indices in shuffle model. (#1710)

* add indexs in shuffle model.

* fix pep

* fix bug

include/LightGBM/boosting.h

@@ -47,7 +47,7 @@ public:
   /*!
   * \brief Shuffle Existing Models
   */
-  virtual void ShuffleModels() = 0;
+  virtual void ShuffleModels(int start_iter, int end_iter) = 0;
 
   virtual void ResetTrainingData(const Dataset* train_data, const ObjectiveFunction* objective_function,
                                  const std::vector<const Metric*>& training_metrics) = 0;

include/LightGBM/c_api.h

@@ -374,7 +374,7 @@ LIGHTGBM_C_EXPORT int LGBM_BoosterFree(BoosterHandle handle);
 /*!
 * \brief Shuffle Models
 */
-LIGHTGBM_C_EXPORT int LGBM_BoosterShuffleModels(BoosterHandle handle);
+LIGHTGBM_C_EXPORT int LGBM_BoosterShuffleModels(BoosterHandle handle, int start_iter, int end_iter);
 
 /*!
 * \brief Merge model in two booster to first handle

python-package/lightgbm/basic.py

@@ -1945,15 +1945,26 @@ class Booster(object):
         _save_pandas_categorical(filename, self.pandas_categorical)
         return self
 
-    def shuffle_models(self):
+    def shuffle_models(self, start_iteration=0, end_iteration=-1):
         """Shuffle models.
 
+        Parameters
+        ----------
+        start_iteration : int, optional (default=0)
+            Index of the iteration that will start to shuffle.
+        end_iteration : int, optional (default=-1)
+            The last iteration that will be shuffled.
+            If <= 0, means the last iteration.
+
         Returns
         -------
         self : Booster
             Booster with shuffled models.
         """
-        _safe_call(_LIB.LGBM_BoosterShuffleModels(self.handle))
+        _safe_call(_LIB.LGBM_BoosterShuffleModels(
+            self.handle,
+            ctypes.c_int(start_iter),
+            ctypes.c_int(end_iter)))
         return self
 
     def model_from_string(self, model_str, verbose=True):

src/boosting/gbdt.h

@@ -70,16 +70,21 @@ public:
     num_iteration_for_pred_ = static_cast<int>(models_.size()) / num_tree_per_iteration_;
   }
 
-  void ShuffleModels() override {
+  void ShuffleModels(int start_iter, int end_iter) override {
     int total_iter = static_cast<int>(models_.size()) / num_tree_per_iteration_;
+    start_iter = std::max(0, start_iter);
+    if (end_iter <= 0) {
+      end_iter = total_iter;
+    }
+    end_iter = std::min(total_iter, end_iter);
     auto original_models = std::move(models_);
     std::vector<int> indices(total_iter);
     for (int i = 0; i < total_iter; ++i) {
       indices[i] = i;
     }
     Random tmp_rand(17);
-    for (int i = 0; i < total_iter - 1; ++i) {
-      int j = tmp_rand.NextShort(i + 1, total_iter);
+    for (int i = start_iter; i < end_iter - 1; ++i) {
+      int j = tmp_rand.NextShort(i + 1, end_iter);
       std::swap(indices[i], indices[j]);
     }
     models_ = std::vector<std::unique_ptr<Tree>>();

src/c_api.cpp

@@ -294,9 +294,9 @@ public:
     dynamic_cast<GBDTBase*>(boosting_.get())->SetLeafValue(tree_idx, leaf_idx, val);
   }
 
-  void ShuffleModels() {
+  void ShuffleModels(int start_iter, int end_iter) {
     std::lock_guard<std::mutex> lock(mutex_);
-    boosting_->ShuffleModels();
+    boosting_->ShuffleModels(start_iter, end_iter);
   }
 
   int GetEvalCounts() const {
@@ -919,10 +919,10 @@ int LGBM_BoosterFree(BoosterHandle handle) {
   API_END();
 }
 
-int LGBM_BoosterShuffleModels(BoosterHandle handle) {
+int LGBM_BoosterShuffleModels(BoosterHandle handle, int start_iter, int end_iter) {
   API_BEGIN();
   Booster* ref_booster = reinterpret_cast<Booster*>(handle);
-  ref_booster->ShuffleModels();
+  ref_booster->ShuffleModels(start_iter, end_iter);
   API_END();
 }