added feature importance to JSON dump (#2656)

* added feature importance to JSON dump

* hotfix

* Update gbdt_model_text.cpp

src/boosting/gbdt_model_text.cpp

@@ -27,11 +27,12 @@ std::string GBDT::DumpModel(int start_iteration, int num_iteration) const {
   str_buf << "\"num_tree_per_iteration\":" << num_tree_per_iteration_ << "," << '\n';
   str_buf << "\"label_index\":" << label_idx_ << "," << '\n';
   str_buf << "\"max_feature_idx\":" << max_feature_idx_ << "," << '\n';
-  str_buf << "\"average_output\":" << (average_output_ ? "true" : "false") << ",\n";
   if (objective_function_ != nullptr) {
     str_buf << "\"objective\":\"" << objective_function_->ToString() << "\",\n";
   }
 
+  str_buf << "\"average_output\":" << (average_output_ ? "true" : "false") << ",\n";
+
   str_buf << "\"feature_names\":[\"" << Common::Join(feature_names_, "\",\"")
           << "\"]," << '\n';
 
@@ -57,7 +58,26 @@ std::string GBDT::DumpModel(int start_iteration, int num_iteration) const {
     str_buf << models_[i]->ToJSON();
     str_buf << "}";
   }
-  str_buf << "]" << '\n';
+  str_buf << "]," << '\n';
+
+  std::vector<double> feature_importances = FeatureImportance(num_iteration, 0);
+  // store the importance first
+  std::vector<std::pair<size_t, std::string>> pairs;
+  for (size_t i = 0; i < feature_importances.size(); ++i) {
+    size_t feature_importances_int = static_cast<size_t>(feature_importances[i]);
+    if (feature_importances_int > 0) {
+      pairs.emplace_back(feature_importances_int, feature_names_[i]);
+    }
+  }
+  str_buf << '\n' << "\"feature_importances\":" << "{";
+  if (!pairs.empty()) {
+    str_buf << "\"" << pairs[0].second << "\":" << std::to_string(pairs[0].first);
+    for (size_t i = 1; i < pairs.size(); ++i) {
+      str_buf << ",";
+      str_buf << "\"" << pairs[i].second << "\":" << std::to_string(pairs[i].first);
+    }
+  }
+  str_buf << "}" << '\n';
 
   str_buf << "}" << '\n';
 
@@ -325,7 +345,7 @@ std::string GBDT::SaveModelToString(int start_iteration, int num_iteration) cons
                       const std::pair<size_t, std::string>& rhs) {
     return lhs.first > rhs.first;
   });
-  ss << '\n' << "feature importances:" << '\n';
+  ss << '\n' << "feature_importances:" << '\n';
   for (size_t i = 0; i < pairs.size(); ++i) {
     ss << pairs[i].second << "=" << std::to_string(pairs[i].first) << '\n';
   }