diff --git a/src/learner.cc b/src/learner.cc
index d5e891c738e9..24932b9279f2 100644
--- a/src/learner.cc
+++ b/src/learner.cc
@@ -729,8 +729,7 @@ class LearnerIO : public LearnerConfiguration {
   std::string const serialisation_header_ { u8"CONFIG-offset:" };
 
  public:
-  explicit LearnerIO(std::vector<std::shared_ptr<DMatrix> > cache) :
-      LearnerConfiguration{cache} {}
+  explicit LearnerIO(std::vector<std::shared_ptr<DMatrix>> cache) : LearnerConfiguration{cache} {}
 
   void LoadModel(Json const& in) override {
     CHECK(IsA<Object>(in));
@@ -754,8 +753,8 @@ class LearnerIO : public LearnerConfiguration {
     auto const& gradient_booster = learner.at("gradient_booster");
     name = get<String>(gradient_booster["name"]);
     tparam_.UpdateAllowUnknown(Args{{"booster", name}});
-    gbm_.reset(GradientBooster::Create(tparam_.booster,
-                                       &generic_parameters_, &learner_model_param_));
+    gbm_.reset(
+        GradientBooster::Create(tparam_.booster, &generic_parameters_, &learner_model_param_));
     gbm_->LoadModel(gradient_booster);
 
     auto const& j_attributes = get<Object const>(learner.at("attributes"));
@@ -767,20 +766,17 @@ class LearnerIO : public LearnerConfiguration {
     // feature names and types are saved in xgboost 1.4
     auto it = learner.find("feature_names");
     if (it != learner.cend()) {
-      auto const &feature_names = get<Array const>(it->second);
-      feature_names_.clear();
-      for (auto const &name : feature_names) {
-        feature_names_.emplace_back(get<String const>(name));
-      }
+      auto const& feature_names = get<Array const>(it->second);
+      feature_names_.resize(feature_names.size());
+      std::transform(feature_names.cbegin(), feature_names.cend(), feature_names_.begin(),
+                     [](Json const& fn) { return get<String const>(fn); });
     }
     it = learner.find("feature_types");
     if (it != learner.cend()) {
-      auto const &feature_types = get<Array const>(it->second);
-      feature_types_.clear();
-      for (auto const &name : feature_types) {
-        auto type = get<String const>(name);
-        feature_types_.emplace_back(type);
-      }
+      auto const& feature_types = get<Array const>(it->second);
+      feature_types_.resize(feature_types.size());
+      std::transform(feature_types.cbegin(), feature_types.cend(), feature_types_.begin(),
+                     [](Json const& fn) { return get<String const>(fn); });
     }
 
     this->need_configuration_ = true;