Implement extend method for meta info.

* Implement extend for host device vector.

include/xgboost/data.h

@@ -158,6 +158,16 @@ class MetaInfo {
    */
   void SetInfo(const char* key, std::string const& interface_str);
 
+  /*
+   * \brief Extend with other MetaInfo.
+   *
+   * \param that The other MetaInfo object.
+   *
+   * \param accumulate_rows Whether rows need to be accumulated in this function.  If
+   *        client code knows number of rows in advance, set this parameter to false.
+   */
+  void Extend(MetaInfo const& that, bool accumulate_rows);
+
  private:
   /*! \brief argsort of labels */
   mutable std::vector<size_t> label_order_cache_;

include/xgboost/host_device_vector.h

@@ -51,6 +51,7 @@
 
 #include <initializer_list>
 #include <vector>
+#include <type_traits>
 
 #include "span.h"
 
@@ -83,6 +84,8 @@ enum GPUAccess {
 
 template <typename T>
 class HostDeviceVector {
+  static_assert(std::is_standard_layout<T>::value, "HostDeviceVector admits only POD types");
+
  public:
   explicit HostDeviceVector(size_t size = 0, T v = T(), int device = -1);
   HostDeviceVector(std::initializer_list<T> init, int device = -1);
@@ -117,6 +120,8 @@ class HostDeviceVector {
   void Copy(const std::vector<T>& other);
   void Copy(std::initializer_list<T> other);
 
+  void Extend(const HostDeviceVector<T>& other);
+
   std::vector<T>& HostVector();
   const std::vector<T>& ConstHostVector() const;
   const std::vector<T>& HostVector() const {return ConstHostVector(); }

src/common/host_device_vector.cc

@@ -136,6 +136,14 @@ void HostDeviceVector<T>::Copy(std::initializer_list<T> other) {
   std::copy(other.begin(), other.end(), HostVector().begin());
 }
 
+template <typename T>
+void HostDeviceVector<T>::Extend(HostDeviceVector const& other) {
+  auto ori_size = this->Size();
+  this->HostVector().resize(ori_size + other.Size());
+  std::copy(other.ConstHostVector().cbegin(), other.ConstHostVector().cend(),
+            this->HostVector().begin() + ori_size);
+}
+
 template <typename T>
 bool HostDeviceVector<T>::HostCanRead() const {
   return true;

src/common/host_device_vector.cu

@@ -125,6 +125,25 @@ class HostDeviceVectorImpl {
     }
   }
 
+  void Extend(HostDeviceVectorImpl* other) {
+    auto ori_size = this->Size();
+    this->Resize(ori_size + other->Size(), T());
+    if (HostCanWrite() && other->HostCanRead()) {
+      auto& h_vec = this->HostVector();
+      auto& other_vec = other->HostVector();
+      CHECK_EQ(h_vec.size(), ori_size + other->Size());
+      std::copy(other_vec.cbegin(), other_vec.cend(), h_vec.begin() + ori_size);
+    } else {
+      auto ptr = other->ConstDevicePointer();
+      SetDevice();
+      CHECK_EQ(this->DeviceIdx(), other->DeviceIdx());
+      dh::safe_cuda(cudaMemcpyAsync(this->DevicePointer() + ori_size,
+                                    ptr,
+                                    other->Size() * sizeof(T),
+                                    cudaMemcpyDeviceToDevice));
+    }
+  }
+
   std::vector<T>& HostVector() {
     LazySyncHost(GPUAccess::kNone);
     return data_h_;
@@ -326,6 +345,11 @@ void HostDeviceVector<T>::Copy(std::initializer_list<T> other) {
   impl_->Copy(other);
 }
 
+template <typename T>
+void HostDeviceVector<T>::Extend(HostDeviceVector const& other) {
+  impl_->Extend(other.impl_);
+}
+
 template <typename T>
 std::vector<T>& HostDeviceVector<T>::HostVector() { return impl_->HostVector(); }
 

src/data/data.cc

@@ -343,6 +343,44 @@ void MetaInfo::SetInfo(const char* key, const void* dptr, DataType dtype, size_t
   }
 }
 
+void MetaInfo::Extend(MetaInfo const& that, bool accumulate_rows) {
+  if (accumulate_rows) {
+    this->num_row_ += that.num_row_;
+  }
+  if (this->num_col_ != 0) {
+    CHECK_EQ(this->num_col_, that.num_col_)
+        << "Number of columns must be consistent across batches.";
+  }
+  this->num_col_ = that.num_col_;
+
+  this->labels_.SetDevice(that.labels_.DeviceIdx());
+  this->labels_.Extend(that.labels_);
+
+  this->weights_.SetDevice(that.weights_.DeviceIdx());
+  this->weights_.Extend(that.weights_);
+
+  this->labels_lower_bound_.SetDevice(that.labels_lower_bound_.DeviceIdx());
+  this->labels_lower_bound_.Extend(that.labels_lower_bound_);
+
+  this->labels_upper_bound_.SetDevice(that.labels_upper_bound_.DeviceIdx());
+  this->labels_upper_bound_.Extend(that.labels_upper_bound_);
+
+  this->base_margin_.SetDevice(that.base_margin_.DeviceIdx());
+  this->base_margin_.Extend(that.base_margin_);
+
+  if (this->group_ptr_.size() == 0) {
+    this->group_ptr_ = that.group_ptr_;
+  } else {
+    CHECK_NE(that.group_ptr_.size(), 0);
+    auto group_ptr = that.group_ptr_;
+    for (size_t i = 1; i < group_ptr.size(); ++i) {
+      group_ptr[i] += this->group_ptr_.back();
+    }
+    this->group_ptr_.insert(this->group_ptr_.end(), group_ptr.begin() + 1,
+                            group_ptr.end());
+  }
+}
+
 void MetaInfo::Validate(int32_t device) const {
   if (group_ptr_.size() != 0 && weights_.Size() != 0) {
     CHECK_EQ(group_ptr_.size(), weights_.Size() + 1)

tests/cpp/data/test_metainfo.cc

@@ -163,3 +163,35 @@ TEST(MetaInfo, Validate) {
   EXPECT_THROW(info.Validate(1), dmlc::Error);
 #endif  // defined(XGBOOST_USE_CUDA)
 }
+
+TEST(MetaInfo, HostExtend) {
+  xgboost::MetaInfo lhs, rhs;
+  size_t const kRows = 100;
+  lhs.labels_.Resize(kRows);
+  lhs.num_row_ = kRows;
+  rhs.labels_.Resize(kRows);
+  rhs.num_row_ = kRows;
+  ASSERT_TRUE(lhs.labels_.HostCanRead());
+  ASSERT_TRUE(rhs.labels_.HostCanRead());
+
+  size_t per_group = 10;
+  std::vector<xgboost::bst_group_t> groups;
+  for (size_t g = 0; g < kRows / per_group; ++g) {
+    groups.emplace_back(per_group);
+  }
+  lhs.SetInfo("group", groups.data(), xgboost::DataType::kUInt32, groups.size());
+  rhs.SetInfo("group", groups.data(), xgboost::DataType::kUInt32, groups.size());
+
+  lhs.Extend(rhs, true);
+  ASSERT_EQ(lhs.num_row_, kRows * 2);
+  ASSERT_TRUE(lhs.labels_.HostCanRead());
+  ASSERT_TRUE(rhs.labels_.HostCanRead());
+  ASSERT_FALSE(lhs.labels_.DeviceCanRead());
+  ASSERT_FALSE(rhs.labels_.DeviceCanRead());
+
+  ASSERT_EQ(lhs.group_ptr_.front(), 0);
+  ASSERT_EQ(lhs.group_ptr_.back(), kRows * 2);
+  for (size_t i = 0; i < kRows * 2 / per_group; ++i) {
+    ASSERT_EQ(lhs.group_ptr_.at(i), per_group * i);
+  }
+}

tests/cpp/data/test_metainfo.cu

@@ -77,7 +77,6 @@ TEST(MetaInfo, FromInterface) {
 
 TEST(MetaInfo, Group) {
   cudaSetDevice(0);
-
   MetaInfo info;
 
   thrust::device_vector<uint32_t> d_uint;
@@ -105,4 +104,25 @@ TEST(MetaInfo, Group) {
   info = MetaInfo();
   EXPECT_ANY_THROW(info.SetInfo("group", float_str.c_str()));
 }
+
+TEST(MetaInfo, DeviceExtend) {
+  dh::safe_cuda(cudaSetDevice(0));
+  size_t const kRows = 100;
+  MetaInfo lhs, rhs;
+
+  thrust::device_vector<float> d_data;
+  std::string str = PrepareData<float>("<f4", &d_data, kRows);
+  lhs.SetInfo("label", str.c_str());
+  rhs.SetInfo("label", str.c_str());
+  ASSERT_FALSE(rhs.labels_.HostCanRead());
+  lhs.num_row_ = kRows;
+  rhs.num_row_ = kRows;
+
+  lhs.Extend(rhs, true);
+  ASSERT_EQ(lhs.num_row_, kRows * 2);
+  ASSERT_FALSE(lhs.labels_.HostCanRead());
+
+  ASSERT_FALSE(lhs.labels_.HostCanRead());
+  ASSERT_FALSE(rhs.labels_.HostCanRead());
+}
 }  // namespace xgboost