Fix empty DMatrix with categorical features.

python-package/xgboost/dask.py

@@ -641,6 +641,8 @@ def next(self, input_data: Callable) -> int:
 
 
 class DaskQuantileDMatrix(DaskDMatrix):
+    """A dask version of :py:class:`QuantileDMatrix`."""
+
     @_deprecate_positional_args
     def __init__(
         self,

src/common/quantile.h

@@ -1,13 +1,12 @@
-/*!
- * Copyright 2014-2022 by XGBoost Contributors
+/**
+ * Copyright 2014-2023 by XGBoost Contributors
  * \file quantile.h
  * \brief util to compute quantiles
  * \author Tianqi Chen
  */
 #ifndef XGBOOST_COMMON_QUANTILE_H_
 #define XGBOOST_COMMON_QUANTILE_H_
 
-#include <dmlc/base.h>
 #include <xgboost/data.h>
 #include <xgboost/logging.h>
 

src/data/iterative_dmatrix.cc

@@ -3,15 +3,20 @@
  */
 #include "iterative_dmatrix.h"
 
-#include <algorithm>  // std::copy
+#include <algorithm>    // std::copy
+#include <cstddef>      // std::size_t
+#include <type_traits>  // std::underlying_type_t
+#include <vector>       // std::vector
 
 #include "../collective/communicator-inl.h"
 #include "../common/categorical.h"  // common::IsCat
 #include "../common/column_matrix.h"
-#include "../tree/param.h"        // FIXME(jiamingy): Find a better way to share this parameter.
+#include "../tree/param.h"  // FIXME(jiamingy): Find a better way to share this parameter.
 #include "gradient_index.h"
 #include "proxy_dmatrix.h"
 #include "simple_batch_iterator.h"
+#include "xgboost/data.h"  // FeatureType
+#include "xgboost/logging.h"
 
 namespace xgboost {
 namespace data {
@@ -79,6 +84,27 @@ void GetCutsFromRef(std::shared_ptr<DMatrix> ref_, bst_feature_t n_features, Bat
       << "Invalid ref DMatrix, different number of features.";
 }
 
+namespace {
+// Synchronize feature type in case of empty DMatrix
+void SyncFeatureType(std::vector<FeatureType>* p_h_ft) {
+  if (!collective::IsDistributed()) {
+    return;
+  }
+  auto& h_ft = *p_h_ft;
+  auto n_ft = h_ft.size();
+  collective::Allreduce<collective::Operation::kMax>(&n_ft, 1);
+  if (!h_ft.empty()) {
+    // Check correct size if this is not an empty DMatrix.
+    CHECK_EQ(h_ft.size(), n_ft);
+  }
+  if (n_ft > 0) {
+    h_ft.resize(n_ft);
+    auto ptr = reinterpret_cast<std::underlying_type_t<FeatureType>*>(h_ft.data());
+    collective::Allreduce<collective::Operation::kMax>(ptr, h_ft.size());
+  }
+}
+}  // anonymous namespace
+
 void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
                                    std::shared_ptr<DMatrix> ref) {
   DMatrixProxy* proxy = MakeProxy(proxy_);
@@ -96,13 +122,14 @@ void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
     return HostAdapterDispatch(proxy, [](auto const& value) { return value.NumCols(); });
   };
 
-  std::vector<size_t> column_sizes;
+  std::vector<std::size_t> column_sizes;
   auto const is_valid = data::IsValidFunctor{missing};
   auto nnz_cnt = [&]() {
     return HostAdapterDispatch(proxy, [&](auto const& value) {
       size_t n_threads = ctx_.Threads();
       size_t n_features = column_sizes.size();
-      linalg::Tensor<size_t, 2> column_sizes_tloc({n_threads, n_features}, Context::kCpuId);
+      linalg::Tensor<std::size_t, 2> column_sizes_tloc({n_threads, n_features}, Context::kCpuId);
+      column_sizes_tloc.Data()->Fill(0ul);
       auto view = column_sizes_tloc.HostView();
       common::ParallelFor(value.Size(), n_threads, common::Sched::Static(256), [&](auto i) {
         auto const& line = value.GetLine(i);
@@ -139,7 +166,8 @@ void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
     if (n_features == 0) {
       n_features = num_cols();
       collective::Allreduce<collective::Operation::kMax>(&n_features, 1);
-      column_sizes.resize(n_features);
+      column_sizes.clear();
+      column_sizes.resize(n_features, 0);
       info_.num_col_ = n_features;
     } else {
       CHECK_EQ(n_features, num_cols()) << "Inconsistent number of columns.";
@@ -166,14 +194,18 @@ void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
    * Generate quantiles
    */
   accumulated_rows = 0;
+  std::vector<FeatureType> h_ft;
   if (ref) {
     GetCutsFromRef(ref, Info().num_col_, batch_param_, &cuts);
+    h_ft = ref->Info().feature_types.HostVector();
   } else {
     size_t i = 0;
     while (iter.Next()) {
       if (!p_sketch) {
+        h_ft = proxy->Info().feature_types.ConstHostVector();
+        SyncFeatureType(&h_ft);
         p_sketch.reset(new common::HostSketchContainer{
-            batch_param_.max_bin, proxy->Info().feature_types.ConstHostSpan(), column_sizes, false,
+            batch_param_.max_bin, h_ft, column_sizes, false,
             proxy->Info().data_split_mode == DataSplitMode::kCol, ctx_.Threads()});
       }
       HostAdapterDispatch(proxy, [&](auto const& batch) {
@@ -191,6 +223,9 @@ void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
     CHECK(p_sketch);
     p_sketch->MakeCuts(&cuts);
   }
+  if (!h_ft.empty()) {
+    CHECK_EQ(h_ft.size(), n_features);
+  }
 
   /**
    * Generate gradient index.
@@ -202,8 +237,7 @@ void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
   while (iter.Next()) {
     HostAdapterDispatch(proxy, [&](auto const& batch) {
       proxy->Info().num_nonzero_ = batch_nnz[i];
-      this->ghist_->PushAdapterBatch(&ctx_, rbegin, prev_sum, batch, missing,
-                                     proxy->Info().feature_types.ConstHostSpan(),
+      this->ghist_->PushAdapterBatch(&ctx_, rbegin, prev_sum, batch, missing, h_ft,
                                      batch_param_.sparse_thresh, Info().num_row_);
     });
     if (n_batches != 1) {
@@ -236,6 +270,8 @@ void IterativeDMatrix::InitFromCPU(DataIterHandle iter_handle, float missing,
     this->info_.num_col_ = n_features;  // proxy might be empty.
     CHECK_EQ(proxy->Info().labels.Size(), 0);
   }
+
+  Info().feature_types.HostVector() = h_ft;
 }
 
 BatchSet<GHistIndexMatrix> IterativeDMatrix::GetGradientIndex(BatchParam const& param) {

tests/test_distributed/test_gpu_with_dask/test_gpu_with_dask.py

@@ -265,6 +265,27 @@ def test_gpu_hist(
     ) -> None:
         run_gpu_hist(params, num_rounds, dataset, dmatrix_type, local_cuda_client)
 
+    def test_empty_quantile_dmatrix(self, local_cuda_client: Client) -> None:
+        client = local_cuda_client
+        X, y = make_categorical(client, 1, 30, 13)
+        X_valid, y_valid = make_categorical(client, 10000, 30, 13)
+
+        Xy = xgb.dask.DaskQuantileDMatrix(client, X, y, enable_categorical=True)
+        Xy_valid = xgb.dask.DaskQuantileDMatrix(
+            client, X_valid, y_valid, ref=Xy, enable_categorical=True
+        )
+        result = xgb.dask.train(
+            client,
+            {"tree_method": "gpu_hist"},
+            Xy,
+            num_boost_round=10,
+            evals=[(Xy_valid, "Valid")],
+        )
+        predt = xgb.dask.inplace_predict(client, result["booster"], X).compute()
+        np.testing.assert_allclose(y.compute(), predt)
+        rmse = result["history"]["Valid"]["rmse"][-1]
+        assert rmse < 32.0
+
     @pytest.mark.skipif(**tm.no_cupy())
     def test_dask_array(self, local_cuda_client: Client) -> None:
         run_with_dask_array(dxgb.DaskDMatrix, local_cuda_client)

tests/test_distributed/test_with_dask/test_with_dask.py

@@ -96,6 +96,9 @@ def pack(**kwargs: Any) -> dd.DataFrame:
         l_n_samples = min(
             n_samples // n_workers, n_samples - i * (n_samples // n_workers)
         )
+        # make sure there's at least one sample for testing empty DMatrix
+        if n_samples == 1 and i == 0:
+            l_n_samples = 1
         future = client.submit(
             pack,
             n_samples=l_n_samples,
@@ -1480,6 +1483,27 @@ def test_quantile_dmatrix(self, client: Client) -> None:
             quantile_hist["Valid"]["rmse"], dmatrix_hist["Valid"]["rmse"]
         )
 
+    def test_empty_quantile_dmatrix(self, client: Client) -> None:
+        X, y = make_categorical(client, 2, 30, 13)
+        X_valid, y_valid = make_categorical(client, 10000, 30, 13)
+        X_valid, y_valid, _ = deterministic_repartition(client, X_valid, y_valid, None)
+
+        Xy = xgb.dask.DaskQuantileDMatrix(client, X, y, enable_categorical=True)
+        Xy_valid = xgb.dask.DaskQuantileDMatrix(
+            client, X_valid, y_valid, ref=Xy, enable_categorical=True
+        )
+        result = xgb.dask.train(
+            client,
+            {"tree_method": "hist"},
+            Xy,
+            num_boost_round=10,
+            evals=[(Xy_valid, "Valid")],
+        )
+        predt = xgb.dask.inplace_predict(client, result["booster"], X).compute()
+        np.testing.assert_allclose(y.compute(), predt)
+        rmse = result["history"]["Valid"]["rmse"][-1]
+        assert rmse < 32.0
+
     @given(params=hist_parameter_strategy, dataset=tm.dataset_strategy)
     @settings(
         deadline=None, max_examples=10, suppress_health_check=suppress, print_blob=True