case when improvement: avoid copy_if_else

src/main/cpp/CMakeLists.txt

@@ -181,6 +181,7 @@ set(CUDFJNI_INCLUDE_DIRS
 add_library(
   spark_rapids_jni SHARED
   src/BloomFilterJni.cpp
+  src/CaseWhenJni.cpp
   src/CastStringJni.cpp
   src/DateTimeRebaseJni.cpp
   src/DecimalUtilsJni.cpp
@@ -196,6 +197,7 @@ add_library(
   src/SparkResourceAdaptorJni.cpp
   src/ZOrderJni.cpp
   src/bloom_filter.cu
+  src/case_when.cu
   src/cast_decimal_to_string.cu
   src/format_float.cu
   src/cast_float_to_string.cu

src/main/cpp/src/CaseWhenJni.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2024, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "case_when.hpp"
+#include "cudf_jni_apis.hpp"
+
+extern "C" {
+
+JNIEXPORT jlong JNICALL Java_com_nvidia_spark_rapids_jni_CaseWhen_selectFirstTrueIndex(
+  JNIEnv* env, jclass, jlongArray bool_cols)
+{
+  JNI_NULL_CHECK(env, bool_cols, "array of column handles is null", 0);
+  try {
+    cudf::jni::auto_set_device(env);
+    cudf::jni::native_jpointerArray<cudf::column_view> n_cudf_bool_columns(env, bool_cols);
+    auto bool_column_views = n_cudf_bool_columns.get_dereferenced();
+    return cudf::jni::release_as_jlong(
+      spark_rapids_jni::select_first_true_index(cudf::table_view(bool_column_views)));
+  }
+  CATCH_STD(env, 0);
+}
+}

src/main/cpp/src/case_when.cu

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2024, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "case_when.hpp"
+
+#include <cudf/column/column_factories.hpp>
+#include <cudf/strings/detail/strings_column_factories.cuh>
+#include <cudf/table/table_device_view.cuh>
+#include <cudf/types.hpp>
+
+#include <thrust/transform.h>
+
+namespace spark_rapids_jni {
+namespace detail {
+namespace {
+
+/**
+ * Select the column index for the first true in bool columns for the specified row
+ */
+struct select_first_true_fn {
+  // bool columns stores the results of executing `when` expressions
+  cudf::table_device_view const d_table;
+
+  /**
+   * The number of bool columns is the size of case when branches.
+   * Note: reuturned index may be out of bound, valid bound is [0, col_num)
+   * When returning col_num index, it means final result is NULL value or ELSE value.
+   *
+   * e.g.:
+   * CASE WHEN 'a' THEN 'A' END
+   *   The number of bool columns is 1
+   *   The number of scalars is 1
+   *   Max index is 1 which means using NULL(all when exprs are false).
+   * CASE WHEN 'a' THEN 'A' ELSE '_' END
+   *   The number of bool columns is 1
+   *   The number of scalars is 2
+   *   Max index is also 1 which means using else value '_'
+   */
+  __device__ cudf::size_type operator()(std::size_t row_idx) const
+  {
+    auto col_num = d_table.num_columns();
+    for (auto col_idx = 0; col_idx < col_num; col_idx++) {
+      auto const& col = d_table.column(col_idx);
+      if (!col.is_null(row_idx) && col.element<bool>(row_idx)) {
+        // Predicate is true and not null
+        return col_idx;
+      }
+    }
+    return col_num;
+  }
+};
+
+}  // anonymous namespace
+
+std::unique_ptr<cudf::column> select_first_true_index(cudf::table_view const& when_bool_columns,
+                                                      rmm::cuda_stream_view stream,
+                                                      rmm::device_async_resource_ref mr)
+{
+  // checks
+  auto const num_columns = when_bool_columns.num_columns();
+  CUDF_EXPECTS(num_columns > 0, "At least one column must be specified");
+  auto const row_count = when_bool_columns.num_rows();
+  if (row_count == 0) {  // empty begets empty
+    return cudf::make_empty_column(cudf::type_id::INT32);
+  }
+  // make output column
+  auto ret = cudf::make_numeric_column(
+    cudf::data_type{cudf::type_id::INT32}, row_count, cudf::mask_state::UNALLOCATED, stream, mr);
+
+  // select first true index
+  auto const d_table_ptr = cudf::table_device_view::create(when_bool_columns, stream);
+  thrust::transform(rmm::exec_policy(stream),
+                    thrust::make_counting_iterator<cudf::size_type>(0),
+                    thrust::make_counting_iterator<cudf::size_type>(row_count),
+                    ret->mutable_view().begin<cudf::size_type>(),
+                    select_first_true_fn{*d_table_ptr});
+  return ret;
+}
+
+}  // namespace detail
+
+std::unique_ptr<cudf::column> select_first_true_index(cudf::table_view const& when_bool_columns,
+                                                      rmm::cuda_stream_view stream,
+                                                      rmm::device_async_resource_ref mr)
+{
+  return detail::select_first_true_index(when_bool_columns, stream, mr);
+}
+
+}  // namespace spark_rapids_jni

src/main/cpp/src/case_when.hpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2024, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cudf/table/table_view.hpp>
+#include <cudf/utilities/default_stream.hpp>
+
+#include <rmm/mr/device/per_device_resource.hpp>
+#include <rmm/resource_ref.hpp>
+
+#include <memory>
+
+namespace spark_rapids_jni {
+
+/**
+ *
+ * Select the column index for the first true in bool columns.
+ * For the row does not contain true, use end index(number of columns).
+ *
+ * e.g.:
+ *   column 0 in table: true,  false, false, false
+ *   column 1 in table: false, true,  false, false
+ *   column 2 in table: false, false, true, false
+ *
+ *   1st row is: true, flase, false; first true index is 0
+ *   2nd row is: false, true, false; first true index is 1
+ *   3rd row is: false, flase, true; first true index is 2
+ *   4th row is: false, false, false; do not find true, set index to the end index 3
+ *
+ *   output column: 0, 1, 2, 3
+ *   In the `case when` context, here 3 index means using NULL value.
+ *
+ */
+std::unique_ptr<cudf::column> select_first_true_index(
+  cudf::table_view const& when_bool_columns,
+  rmm::cuda_stream_view stream      = cudf::get_default_stream(),
+  rmm::device_async_resource_ref mr = rmm::mr::get_current_device_resource());
+
+}  // namespace spark_rapids_jni

src/main/java/com/nvidia/spark/rapids/jni/CaseWhen.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2024, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.nvidia.spark.rapids.jni;
+
+import ai.rapids.cudf.*;
+
+
+/**
+ * Exedute SQL `case when` semantic.
+ * If there are multiple branches and each branch uses scalar to generator value,
+ * then it's fast to use this class because it does not generate temp string columns.
+ *
+ * E.g.:
+ *   SQL is:
+ *     select
+ *        case
+ *          when bool_1_expr then "value_1"
+ *          when bool_2_expr then "value_2"
+ *          when bool_3_expr then "value_3"
+ *          else "value_else"
+ *        end
+ *      from tab
+ *
+ * Execution steps:
+ *   Execute bool exprs to get bool columns, e.g., gets:
+ *     bool column 1: [true,  false, false, false]  // bool_1_expr result
+ *     bool column 2: [false, true,  false, flase]  // bool_2_expr result
+ *     bool column 3: [false, false, true,  flase]  // bool_3_expr result
+ *   Execute `selectFirstTrueIndex` to get the column index for the first true in bool columns.
+ *   Generate a column to store salars: "value_1", "value_2", "value_3", "value_else"
+ *   Execute `Table.gather` to generate the final output column
+ *
+ */
+public class CaseWhen {
+
+  /**
+   *
+   * Select the column index for the first true in bool columns.
+   * For the row does not contain true, use end index(number of columns).
+   *
+   * e.g.:
+   *   column 0: true,  false, false, false
+   *   column 1: false, true,  false, false
+   *   column 2: false, false, true, false
+   *
+   *   1st row is: true, flase, false; first true index is 0
+   *   2nd row is: false, true, false; first true index is 1
+   *   3rd row is: false, flase, true; first true index is 2
+   *   4th row is: false, false, false; do not find true, set index to the end index 3
+   *
+   *   output column: 0, 1, 2, 3
+   *   In the `case when` context, here 3 index means using NULL value.
+   *
+  */
+  public static ColumnVector selectFirstTrueIndex(ColumnVector[] boolColumns) {
+    for (ColumnVector cv : boolColumns) {
+      assert(cv.getType().equals(DType.BOOL8)) : "Columns must be bools";
+    }
+
+    long[] boolHandles = new long[boolColumns.length];
+    for (int i = 0; i < boolColumns.length; ++i) {
+      boolHandles[i] = boolColumns[i].getNativeView();
+    }
+
+    return new ColumnVector(selectFirstTrueIndex(boolHandles));
+  }
+
+  private static native long selectFirstTrueIndex(long[] boolHandles);
+}

src/test/java/com/nvidia/spark/rapids/jni/CaseWhenTest.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2024, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.nvidia.spark.rapids.jni;
+
+import ai.rapids.cudf.*;
+
+import org.junit.jupiter.api.Test;
+
+import static ai.rapids.cudf.AssertUtils.assertColumnsAreEqual;
+
+public class CaseWhenTest {
+
+  @Test
+  void selectIndexTest() {
+    try (
+        ColumnVector b0 = ColumnVector.fromBooleans(
+            true, false, false, false);
+        ColumnVector b1 = ColumnVector.fromBooleans(
+            true, true, false, false);
+        ColumnVector b2 = ColumnVector.fromBooleans(
+            false, false, true, false);
+        ColumnVector b3 = ColumnVector.fromBooleans(
+            true, true, true, false);
+        ColumnVector expected = ColumnVector.fromInts(0, 1, 2, 4)) {
+      ColumnVector[] boolColumns = new ColumnVector[] { b0, b1, b2, b3 };
+      try (ColumnVector actual = CaseWhen.selectFirstTrueIndex(boolColumns)) {
+        assertColumnsAreEqual(expected, actual);
+      }
+    }
+  }
+
+  @Test
+  void selectIndexTestWithNull() {
+    try (
+        ColumnVector b0 = ColumnVector.fromBoxedBooleans(
+            null, false, false, null, false);
+        ColumnVector b1 = ColumnVector.fromBoxedBooleans(
+            null, null, false, true, true);
+        ColumnVector b2 = ColumnVector.fromBoxedBooleans(
+            null, null, false, true, false);
+        ColumnVector b3 = ColumnVector.fromBoxedBooleans(
+            null, null, null, true, null);
+        ColumnVector expected = ColumnVector.fromInts(4, 4, 4, 1, 1)) {
+      ColumnVector[] boolColumns = new ColumnVector[] { b0, b1, b2, b3 };
+      try (ColumnVector actual = CaseWhen.selectFirstTrueIndex(boolColumns)) {
+        assertColumnsAreEqual(expected, actual);
+      }
+    }
+  }
+}