refine early-stopping feature (#27)

* change Print to PrintAndGetLoss: return loss

include/LightGBM/metric.h

@@ -32,7 +32,7 @@ public:
   * \param iter Current iteration
   * \param score Current prediction score
   */
-  virtual void Print(int iter, const score_t* score, score_t& loss) const = 0;
+  virtual score_t PrintAndGetLoss(int iter, const score_t* score) const = 0;
 
   /*!
   * \brief Create object of metrics

src/boosting/gbdt.cpp

@@ -239,16 +239,15 @@ void GBDT::UpdateScore(const Tree* tree) {
 }
 
 bool GBDT::OutputMetric(int iter) {
-  score_t train_score_ = 0, test_score_ = 0; 
   bool ret = false;
   // print training metric
   for (auto& sub_metric : training_metrics_) {
-    sub_metric->Print(iter, train_score_updater_->score(), train_score_);
+    sub_metric->PrintAndGetLoss(iter, train_score_updater_->score());
   }
   // print validation metric
   for (size_t i = 0; i < valid_metrics_.size(); ++i) {
     for (size_t j = 0; j < valid_metrics_[i].size(); ++j) {
-      valid_metrics_[i][j]->Print(iter, valid_score_updater_[i]->score(), test_score_);
+      score_t test_score_ = valid_metrics_[i][j]->PrintAndGetLoss(iter, valid_score_updater_[i]->score());
       if (!ret && early_stopping_round_ > 0){
         bool the_bigger_the_better_ = valid_metrics_[i][j]->the_bigger_the_better;
         if (best_score_[i][j] < 0 

src/metric/binary_metric.hpp

@@ -50,7 +50,7 @@ public:
     }
   }
 
-  void Print(int iter, const score_t* score, score_t& loss) const override {
+  score_t PrintAndGetLoss(int iter, const score_t* score) const override {
     score_t sum_loss = 0.0f;
     if (early_stopping_round_ > 0 || (output_freq_ > 0 && iter % output_freq_ == 0)) {
       if (weights_ == nullptr) {
@@ -70,11 +70,13 @@ public:
           sum_loss += PointWiseLossCalculator::LossOnPoint(label_[i], prob) * weights_[i];
         }
       }
-      loss = sum_loss / sum_weights_;
+      score_t loss = sum_loss / sum_weights_;
       if (output_freq_ > 0 && iter % output_freq_ == 0){
         Log::Stdout("Iteration:%d, %s's %s: %f", iter, name, PointWiseLossCalculator::Name(), loss);
       }
+      return loss;
     }
+    return 0.0f;
   }
 
 private:
@@ -170,7 +172,7 @@ public:
     }
   }
 
-  void Print(int iter, const score_t* score, score_t& loss) const override {
+  score_t PrintAndGetLoss(int iter, const score_t* score) const override {
     if (early_stopping_round_ > 0 || (output_freq_ > 0 && iter % output_freq_ == 0)) {
       // get indices sorted by score, descent order
       std::vector<data_size_t> sorted_idx;
@@ -227,11 +229,12 @@ public:
       if (sum_pos > 0.0f && sum_pos != sum_weights_) {
         auc = accum / (sum_pos *(sum_weights_ - sum_pos));
       }
-      loss = auc;
       if (output_freq_ > 0 && iter % output_freq_ == 0){
-        Log::Stdout("iteration:%d, %s's %s: %f", iter, name, "auc", loss);
+        Log::Stdout("iteration:%d, %s's %s: %f", iter, name, "auc", auc);
       }
+      return auc;
     }
+    return 0.0f;
   }
 
 private:

src/metric/rank_metric.hpp

@@ -75,7 +75,7 @@ public:
     }
   }
 
-  void Print(int iter, const score_t* score, score_t& loss) const override {
+  score_t PrintAndGetLoss(int iter, const score_t* score) const override {
     if (early_stopping_round_ > 0 || (output_freq_ > 0 && iter % output_freq_ == 0)) {
       // some buffers for multi-threading sum up
       std::vector<std::vector<double>> result_buffer_;
@@ -134,11 +134,12 @@ public:
         result[j] /= sum_query_weights_;
         result_ss << "NDCG@" << eval_at_[j] << ":" << result[j] << "\t";
       }
-      loss = result[0];
       if (output_freq_ > 0 && iter % output_freq_ == 0){
         Log::Stdout("Iteration:%d, Test:%s, %s ", iter, name, result_ss.str().c_str());
       }
+      return result[0];
     }
+    return 0.0f;
   }
 
 private:

src/metric/regression_metric.hpp

@@ -42,7 +42,7 @@ public:
     }
   }
   
-  void Print(int iter, const score_t* score, score_t& loss) const override {
+  score_t PrintAndGetLoss(int iter, const score_t* score) const override {
     if (early_stopping_round_ > 0 || (output_freq_ > 0 && iter % output_freq_ == 0)) {
       score_t sum_loss = 0.0;
       if (weights_ == nullptr) {
@@ -58,11 +58,13 @@ public:
           sum_loss += PointWiseLossCalculator::LossOnPoint(label_[i], score[i]) * weights_[i];
         }
       }
-      loss = PointWiseLossCalculator::AverageLoss(sum_loss, sum_weights_);
+      score_t loss = PointWiseLossCalculator::AverageLoss(sum_loss, sum_weights_);
       if (output_freq_ > 0 && iter % output_freq_ == 0){
         Log::Stdout("Iteration:%d, %s's %s : %f", iter, name, PointWiseLossCalculator::Name(), loss);
       }
+      return loss;
     }
+    return 0.0f;
   }
 
   inline static score_t AverageLoss(score_t sum_loss, score_t sum_weights) {