removed warnings about types in comparison ([-Wsign-compare]) (#1953)

* removed comparison warning

* fixed spacing

src/io/dataset.cpp

@@ -158,7 +158,7 @@ std::vector<std::vector<int>> FastFeatureBundling(std::vector<std::unique_ptr<Bi
   // sort by non zero cnt
   std::vector<int> sorted_idx;
   sorted_idx.reserve(used_features.size());
-  for (int i = 0; i < used_features.size(); ++i) {
+  for (int i = 0; i < static_cast<int>(used_features.size()); ++i) {
     sorted_idx.emplace_back(i);
   }
   // sort by non zero cnt, bigger first

src/io/dataset_loader.cpp

@@ -371,7 +371,7 @@ Dataset* DatasetLoader::LoadFromBinFile(const char* data_filename, const char* b
   mem_ptr += sizeof(int) * (dataset->num_groups_);
 
   if(!config_.monotone_constraints.empty()) {
-    CHECK(dataset->num_total_features_ == config_.monotone_constraints.size());
+    CHECK(static_cast<size_t>(dataset->num_total_features_) == config_.monotone_constraints.size());
     dataset->monotone_types_.resize(dataset->num_features_);
     for(int i = 0; i < dataset->num_total_features_; ++i){
       int inner_fidx = dataset->InnerFeatureIndex(i);
@@ -394,7 +394,7 @@ Dataset* DatasetLoader::LoadFromBinFile(const char* data_filename, const char* b
   }
 
   if(!config_.feature_contri.empty()) {
-    CHECK(dataset->num_total_features_ == config_.feature_contri.size());
+    CHECK(static_cast<size_t>(dataset->num_total_features_) == config_.feature_contri.size());
     dataset->feature_penalty_.resize(dataset->num_features_);
     for(int i = 0; i < dataset->num_total_features_; ++i){
       int inner_fidx = dataset->InnerFeatureIndex(i);

src/metric/dcg_calculator.cpp

@@ -39,7 +39,7 @@ void DCGCalculator::DefaultLabelGain(std::vector<double>* label_gain) {
 
 void DCGCalculator::Init(const std::vector<double>& input_label_gain) {
   label_gain_.resize(input_label_gain.size());
-  for(size_t i = 0;i < input_label_gain.size();++i){
+  for (size_t i = 0; i < input_label_gain.size(); ++i) {
     label_gain_[i] = static_cast<double>(input_label_gain[i]);
   }
   discount_.resize(kMaxPosition);