Add Java/JNI applyNullMask to ColumnView

java/src/main/java/ai/rapids/cudf/ColumnView.java

@@ -630,6 +630,28 @@ public final ColumnVector ifElse(Scalar trueValue, Scalar falseValue) {
     return new ColumnVector(result);
   }
 
+  /**
+   * Returns a copy of this column with each row set to null wherever the corresponding row
+   * in booleanMask is false or null, leaving the other rows as they already are (including
+   * any that were already null).
+   * <p>
+   * This is a convenience over {@code ifElse}, which otherwise needs a null scalar of this
+   * column's type constructed just to null out the false rows.
+   * @param booleanMask a BOOL8 column with the same row count as this column
+   * @return a new column with this column's values, nulled out where booleanMask is not true
+   */
+  public final ColumnVector applyNullMask(ColumnView booleanMask) {
+    if (!booleanMask.getType().equals(DType.BOOL8)) {
+      throw new IllegalArgumentException("Mask column must be of type BOOL8, found " +
+          booleanMask.getType());
+    }
+    if (booleanMask.getRowCount() != getRowCount()) {
+      throw new IllegalArgumentException("Mask column row count (" + booleanMask.getRowCount() +
+          ") does not match this column's row count (" + getRowCount() + ")");
+    }
+    return new ColumnVector(applyNullMask(getNativeView(), booleanMask.getNativeView()));
+  }
+
   /////////////////////////////////////////////////////////////////////////////
   // Slice/Split and Concatenate
   /////////////////////////////////////////////////////////////////////////////
@@ -5128,6 +5150,8 @@ private static native long scan(long viewHandle, long aggregation,
 
   private static native long ifElseSS(long predVec, long trueScalar, long falseScalar) throws CudfException;
 
+  private static native long applyNullMask(long baseHandle, long boolMaskHandle) throws CudfException;
+
   private static native long reduce(long viewHandle, long aggregation, int dtype, int scale) throws CudfException;
 
   private static native long segmentedReduce(long dataViewHandle, long offsetsViewHandle,

java/src/main/native/src/ColumnViewJni.cpp

@@ -303,6 +303,33 @@ JNIEXPORT jlong JNICALL Java_ai_rapids_cudf_ColumnView_ifElseSS(
   JNI_CATCH(env, 0);
 }
 
+JNIEXPORT jlong JNICALL Java_ai_rapids_cudf_ColumnView_applyNullMask(JNIEnv* env,
+                                                                     jclass,
+                                                                     jlong j_col,
+                                                                     jlong j_bool_mask)
+{
+  JNI_NULL_CHECK(env, j_col, "column is null", 0);
+  JNI_NULL_CHECK(env, j_bool_mask, "mask column is null", 0);
+  JNI_TRY
+  {
+    cudf::jni::auto_set_device(env);
+    auto const col_view  = reinterpret_cast<cudf::column_view*>(j_col);
+    auto const mask_view = reinterpret_cast<cudf::column_view*>(j_bool_mask);
+
+    auto [bool_mask, bool_null_count] = cudf::bools_to_mask(*mask_view);
+    auto copy                         = std::make_unique<cudf::column>(*col_view);
+    auto result                       = cudf::structs::detail::superimpose_and_sanitize_nulls(
+      static_cast<cudf::bitmask_type const*>(bool_mask->data()),
+      bool_null_count,
+      std::move(copy),
+      cudf::get_default_stream(),
+      cudf::get_current_device_resource_ref());
+
+    return release_as_jlong(result);
+  }
+  JNI_CATCH(env, 0);
+}
+
 JNIEXPORT jlong JNICALL Java_ai_rapids_cudf_ColumnView_getElement(JNIEnv* env,
                                                                   jclass,
                                                                   jlong from,

java/src/test/java/ai/rapids/cudf/IfElseTest.java

@@ -1,6 +1,6 @@
 /*
  *
- *  SPDX-FileCopyrightText: Copyright (c) 2020, NVIDIA CORPORATION.
+ *  SPDX-FileCopyrightText: Copyright (c) 2020-2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
  *  SPDX-License-Identifier: Apache-2.0
  *
  */
@@ -1167,4 +1167,39 @@ void testMismatchedTypesSS() {
       assertThrows(CudfException.class, () -> pred.ifElse(trueScalar, falseScalar));
     }
   }
+
+  @Test
+  void testApplyNullMask() {
+    try (ColumnVector input = ColumnVector.fromBoxedInts(0, 100, 1, 2, Integer.MIN_VALUE, null);
+         ColumnVector mask = ColumnVector.fromBoxedBooleans(true, false, true, null, false, true);
+         ColumnVector result = input.applyNullMask(mask);
+         ColumnVector expected = ColumnVector.fromBoxedInts(0, null, 1, null, null, null)) {
+      assertColumnsAreEqual(expected, result);
+    }
+  }
+
+  @Test
+  void testApplyNullMaskAllTrueIsValuePreserving() {
+    try (ColumnVector input = ColumnVector.fromBoxedInts(0, 100, null, 2);
+         ColumnVector mask = ColumnVector.fromBoxedBooleans(true, true, true, true);
+         ColumnVector result = input.applyNullMask(mask)) {
+      assertColumnsAreEqual(input, result);
+    }
+  }
+
+  @Test
+  void testApplyNullMaskRejectsNonBooleanMask() {
+    try (ColumnVector input = ColumnVector.fromBoxedInts(0, 100, 1, 2);
+         ColumnVector mask = ColumnVector.fromBoxedInts(1, 0, 1, 0)) {
+      assertThrows(IllegalArgumentException.class, () -> input.applyNullMask(mask));
+    }
+  }
+
+  @Test
+  void testApplyNullMaskRejectsRowCountMismatch() {
+    try (ColumnVector input = ColumnVector.fromBoxedInts(0, 100, 1, 2);
+         ColumnVector mask = ColumnVector.fromBoxedBooleans(true, false, true)) {
+      assertThrows(IllegalArgumentException.class, () -> input.applyNullMask(mask));
+    }
+  }
 }