Extract transform iterator. (#8498)

src/data/ellpack_page.cu

@@ -7,6 +7,7 @@
 #include "../common/categorical.h"
 #include "../common/hist_util.cuh"
 #include "../common/random.h"
+#include "../common/transform_iterator.h"  // MakeIndexTransformIter
 #include "./ellpack_page.cuh"
 #include "device_adapter.cuh"
 #include "gradient_index.h"

src/data/gradient_index.cc

@@ -13,6 +13,7 @@
 #include "../common/hist_util.h"
 #include "../common/numeric.h"
 #include "../common/threading_utils.h"
+#include "../common/transform_iterator.h"  // MakeIndexTransformIter
 
 namespace xgboost {
 
@@ -78,7 +79,7 @@ GHistIndexMatrix::~GHistIndexMatrix() = default;
 void GHistIndexMatrix::PushBatch(SparsePage const &batch, common::Span<FeatureType const> ft,
                                  int32_t n_threads) {
   auto page = batch.GetView();
-  auto it = common::MakeIndexTransformIter([&](size_t ridx) { return page[ridx].size(); });
+  auto it = common::MakeIndexTransformIter([&](std::size_t ridx) { return page[ridx].size(); });
   common::PartialSum(n_threads, it, it + page.Size(), static_cast<size_t>(0), row_ptr.begin());
   data::SparsePageAdapterBatch adapter_batch{page};
   auto is_valid = [](auto) { return true; };  // SparsePage always contains valid entries

src/data/gradient_index.h

@@ -15,6 +15,7 @@
 #include "../common/hist_util.h"
 #include "../common/numeric.h"
 #include "../common/threading_utils.h"
+#include "../common/transform_iterator.h"  // MakeIndexTransformIter
 #include "adapter.h"
 #include "proxy_dmatrix.h"
 #include "xgboost/base.h"