[pyspark] Cleanup data processing. (#8344)

* Enable additional combinations of ctor parameters.
* Unify procedures for QuantileDMatrix and DMatrix.

doc/tutorials/spark_estimator.rst

@@ -83,10 +83,11 @@ generate result dataset with 3 new columns:
 XGBoost PySpark GPU support
 ***************************
 
-XGBoost PySpark supports GPU training and prediction. To enable GPU support, you first need
-to install the xgboost and cudf packages. Then you can set `use_gpu` parameter to `True`.
+XGBoost PySpark supports GPU training and prediction. To enable GPU support, first you
+need to install the XGBoost and the `cuDF <https://docs.rapids.ai/api/cudf/stable/>`_
+package. Then you can set `use_gpu` parameter to `True`.
 
-Below tutorial will show you how to train a model with XGBoost PySpark GPU on Spark
+Below tutorial demonstrates how to train a model with XGBoost PySpark GPU on Spark
 standalone cluster.
 
 
@@ -138,7 +139,7 @@ in PySpark. Please refer to
   conda create -y -n xgboost-env -c conda-forge conda-pack python=3.9
   conda activate xgboost-env
   pip install xgboost
-  pip install cudf
+  conda install cudf -c rapids -c nvidia -c conda-forge
   conda pack -f -o xgboost-env.tar.gz
 
 
@@ -220,3 +221,6 @@ Below is a simple example submit command for enabling GPU acceleration:
     --conf spark.sql.execution.arrow.maxRecordsPerBatch=1000000 \
     --archives xgboost-env.tar.gz#environment \
     xgboost_app.py
+
+When rapids plugin is enabled, both of the JVM rapids plugin and the cuDF Python are
+required for the acceleration.

python-package/xgboost/spark/core.py

@@ -747,7 +747,7 @@ def _fit(self, dataset):
             k: v for k, v in train_call_kwargs_params.items() if v is not None
         }
         dmatrix_kwargs = {k: v for k, v in dmatrix_kwargs.items() if v is not None}
-        use_qdm = booster_params.get("tree_method") in ("hist", "gpu_hist")
+        use_qdm = booster_params.get("tree_method", None) in ("hist", "gpu_hist")
 
         def _train_booster(pandas_df_iter):
             """Takes in an RDD partition and outputs a booster for that partition after

python-package/xgboost/spark/data.py

@@ -208,14 +208,27 @@ def create_dmatrix_from_partitions(  # pylint: disable=too-many-arguments
 
     def append_m(part: pd.DataFrame, name: str, is_valid: bool) -> None:
         nonlocal n_features
-        if name in part.columns and part[name].shape[0] > 0:
-            array = part[name]
-            if name == alias.data:
+        if name == alias.data or name in part.columns:
+            if (
+                name == alias.data
+                and feature_cols is not None
+                and part[feature_cols].shape[0] > 0  # guard against empty partition
+            ):
+                array: Optional[np.ndarray] = part[feature_cols]
+            elif part[name].shape[0] > 0:
+                array = part[name]
                 array = stack_series(array)
+            else:
+                array = None
+
+            if name == alias.data and array is not None:
                 if n_features == 0:
                     n_features = array.shape[1]
                 assert n_features == array.shape[1]
 
+            if array is None:
+                return
+
             if is_valid:
                 valid_data[name].append(array)
             else:
@@ -238,26 +251,6 @@ def append_m_sparse(part: pd.DataFrame, name: str, is_valid: bool) -> None:
             else:
                 train_data[name].append(array)
 
-    def append_qdm(part: pd.DataFrame, name: str, is_valid: bool) -> None:
-        """Preprocessing for QuantileDMatrix."""
-        nonlocal n_features
-        if name == alias.data or name in part.columns:
-            if name == alias.data and feature_cols is not None:
-                array = part[feature_cols]
-            else:
-                array = part[name]
-                array = stack_series(array)
-
-            if name == alias.data:
-                if n_features == 0:
-                    n_features = array.shape[1]
-                assert n_features == array.shape[1]
-
-            if is_valid:
-                valid_data[name].append(array)
-            else:
-                train_data[name].append(array)
-
     def make(values: Dict[str, List[np.ndarray]], kwargs: Dict[str, Any]) -> DMatrix:
         if len(values) == 0:
             get_logger("XGBoostPySpark").warning(
@@ -305,13 +298,14 @@ def split_params() -> Tuple[Dict[str, Any], Dict[str, Union[int, float, bool]]]:
 
     meta, params = split_params()
 
-    if feature_cols is not None:  # rapidsai plugin
-        assert gpu_id is not None
-        assert use_qdm is True
-        cache_partitions(iterator, append_qdm)
+    if feature_cols is not None and use_qdm:
+        cache_partitions(iterator, append_fn)
         dtrain: DMatrix = make_qdm(train_data, gpu_id, meta, None, params)
-    elif use_qdm:
-        cache_partitions(iterator, append_qdm)
+    elif feature_cols is not None and not use_qdm:
+        cache_partitions(iterator, append_fn)
+        dtrain = make(train_data, kwargs)
+    elif feature_cols is None and use_qdm:
+        cache_partitions(iterator, append_fn)
         dtrain = make_qdm(train_data, gpu_id, meta, None, params)
     else:
         cache_partitions(iterator, append_fn)

tests/python-gpu/test_gpu_spark/test_data.py

@@ -19,7 +19,9 @@
 
 
 @pytest.mark.skipif(**tm.no_cudf())
-def test_qdm_ctor() -> None:
-    run_dmatrix_ctor(is_dqm=True, on_gpu=True)
-    with pytest.raises(AssertionError):
-        run_dmatrix_ctor(is_dqm=False, on_gpu=True)
+@pytest.mark.parametrize(
+    "is_feature_cols,is_qdm",
+    [(True, True), (True, False), (False, True), (False, False)],
+)
+def test_dmatrix_ctor(is_feature_cols: bool, is_qdm: bool) -> None:
+    run_dmatrix_ctor(is_feature_cols, is_qdm, on_gpu=True)

tests/python/test_spark/test_data.py

@@ -18,6 +18,8 @@
     stack_series,
 )
 
+from xgboost import DMatrix, QuantileDMatrix
+
 
 def test_stack() -> None:
     a = pd.DataFrame({"a": [[1, 2], [3, 4]]})
@@ -37,7 +39,7 @@ def test_stack() -> None:
     assert b.shape == (2, 1)
 
 
-def run_dmatrix_ctor(is_dqm: bool, on_gpu: bool) -> None:
+def run_dmatrix_ctor(is_feature_cols: bool, is_qdm: bool, on_gpu: bool) -> None:
     rng = np.random.default_rng(0)
     dfs: List[pd.DataFrame] = []
     n_features = 16
@@ -57,27 +59,35 @@ def run_dmatrix_ctor(is_dqm: bool, on_gpu: bool) -> None:
         df = pd.DataFrame(
             {alias.label: y, alias.margin: m, alias.weight: w, alias.valid: valid}
         )
-        if on_gpu:
+        if is_feature_cols:
             for j in range(X.shape[1]):
                 df[f"feat-{j}"] = pd.Series(X[:, j])
         else:
             df[alias.data] = pd.Series(list(X))
         dfs.append(df)
 
     kwargs = {"feature_types": feature_types}
-    if on_gpu:
-        cols = [f"feat-{i}" for i in range(n_features)]
-        train_Xy, valid_Xy = create_dmatrix_from_partitions(
-            iter(dfs), cols, 0, is_dqm, kwargs, False, True
-        )
-    elif is_dqm:
-        train_Xy, valid_Xy = create_dmatrix_from_partitions(
-            iter(dfs), None, None, True, kwargs, False, True
-        )
+    device_id = 0 if on_gpu else None
+    cols = [f"feat-{i}" for i in range(n_features)]
+    feature_cols = cols if is_feature_cols else None
+    train_Xy, valid_Xy = create_dmatrix_from_partitions(
+        iter(dfs),
+        feature_cols,
+        gpu_id=device_id,
+        use_qdm=is_qdm,
+        kwargs=kwargs,
+        enable_sparse_data_optim=False,
+        has_validation_col=True,
+    )
+
+    if is_qdm:
+        assert isinstance(train_Xy, QuantileDMatrix)
+        assert isinstance(valid_Xy, QuantileDMatrix)
     else:
-        train_Xy, valid_Xy = create_dmatrix_from_partitions(
-            iter(dfs), None, None, False, kwargs, False, True
-        )
+        assert not isinstance(train_Xy, QuantileDMatrix)
+        assert isinstance(train_Xy, DMatrix)
+        assert not isinstance(valid_Xy, QuantileDMatrix)
+        assert isinstance(valid_Xy, DMatrix)
 
     assert valid_Xy is not None
     assert valid_Xy.num_row() + train_Xy.num_row() == n_samples_per_batch * n_batches
@@ -109,9 +119,12 @@ def run_dmatrix_ctor(is_dqm: bool, on_gpu: bool) -> None:
     np.testing.assert_equal(valid_Xy.feature_types, feature_types)
 
 
-def test_dmatrix_ctor() -> None:
-    run_dmatrix_ctor(is_dqm=False, on_gpu=False)
-    run_dmatrix_ctor(is_dqm=True, on_gpu=False)
+@pytest.mark.parametrize(
+    "is_feature_cols,is_qdm",
+    [(True, True), (True, False), (False, True), (False, False)],
+)
+def test_dmatrix_ctor(is_feature_cols: bool, is_qdm: bool) -> None:
+    run_dmatrix_ctor(is_feature_cols, is_qdm, on_gpu=False)
 
 
 def test_read_csr_matrix_from_unwrapped_spark_vec() -> None: