Start investigating group split.

amalgamation/xgboost-all0.cc

@@ -70,6 +70,7 @@
 #include "../src/logging.cc"
 #include "../src/common/common.cc"
 #include "../src/common/charconv.cc"
+#include "../src/common/categorical.cc"
 #include "../src/common/timer.cc"
 #include "../src/common/host_device_vector.cc"
 #include "../src/common/hist_util.cc"

src/common/categorical.cc

@@ -0,0 +1,12 @@
+/*!
+ * Copyright 2020 by XGBoost Contributors
+ * \file categorical.cc
+ */
+
+#include "categorical.h"
+
+namespace xgboost {
+namespace common {
+DMLC_REGISTER_PARAMETER(CategoricalParam);
+}  // namespace common
+}  // namespace xgboost

src/common/categorical.h

@@ -8,6 +8,7 @@
 #include "xgboost/base.h"
 #include "xgboost/data.h"
 #include "xgboost/span.h"
+#include "xgboost/parameter.h"
 
 namespace xgboost {
 namespace common {
@@ -43,6 +44,17 @@ inline XGBOOST_DEVICE bool GoLeft(float l, float r, bool is_cat, Comp comp) {
   }
   return comp(l, r);
 }
+
+struct CategoricalParam : XGBoostParameter<CategoricalParam> {
+  int32_t max_cat_to_onehot {-1};
+
+  DMLC_DECLARE_PARAMETER(CategoricalParam) {
+    DMLC_DECLARE_FIELD(max_cat_to_onehot)
+        .set_lower_bound(-1)
+        .set_default(-1)
+        .describe("Maximum number of categories for one hot split.");
+  }
+};
 }  // namespace common
 }  // namespace xgboost
 

src/tree/updater_gpu_hist.cu

@@ -865,6 +865,7 @@ class GPUHistMaker : public TreeUpdater {
     // The passed in args can be empty, if we simply purge the old maker without
     // preserving parameters then we can't do Update on it.
     TrainParam param;
+    cat_param_.UpdateAllowUnknown(args);
     if (float_maker_) {
       param = float_maker_->param_;
     } else if (double_maker_) {
@@ -884,6 +885,7 @@ class GPUHistMaker : public TreeUpdater {
   void LoadConfig(Json const& in) override {
     auto const& config = get<Object const>(in);
     FromJson(config.at("gpu_hist_train_param"), &this->hist_maker_param_);
+    FromJson(config.at("categorical_param"), &this->cat_param_);
     if (hist_maker_param_.single_precision_histogram) {
       float_maker_.reset(new GPUHistMakerSpecialised<GradientPair>());
       FromJson(config.at("train_param"), &float_maker_->param_);
@@ -895,6 +897,7 @@ class GPUHistMaker : public TreeUpdater {
   void SaveConfig(Json* p_out) const override {
     auto& out = *p_out;
     out["gpu_hist_train_param"] = ToJson(hist_maker_param_);
+    out["categorical_param"] = ToJson(cat_param_);
     if (hist_maker_param_.single_precision_histogram) {
       out["train_param"] = ToJson(float_maker_->param_);
     } else {
@@ -926,6 +929,7 @@ class GPUHistMaker : public TreeUpdater {
 
  private:
   GPUHistMakerTrainParam hist_maker_param_;
+  common::CategoricalParam cat_param_;
   std::unique_ptr<GPUHistMakerSpecialised<GradientPair>> float_maker_;
   std::unique_ptr<GPUHistMakerSpecialised<GradientPairPrecise>> double_maker_;
 };