Implement interleave_columns for list type

conda/recipes/libcudf/meta.yaml

@@ -135,6 +135,7 @@ test:
     - test -f $PREFIX/include/cudf/lists/detail/concatenate.hpp
     - test -f $PREFIX/include/cudf/lists/detail/copying.hpp
     - test -f $PREFIX/include/cudf/lists/detail/drop_list_duplicates.hpp
+    - test -f $PREFIX/include/cudf/lists/detail/interleave_columns.hpp
     - test -f $PREFIX/include/cudf/lists/detail/sorting.hpp
     - test -f $PREFIX/include/cudf/lists/count_elements.hpp
     - test -f $PREFIX/include/cudf/lists/explode.hpp

cpp/CMakeLists.txt

@@ -268,9 +268,10 @@ add_library(cudf
     src/lists/copying/gather.cu
     src/lists/copying/segmented_gather.cu
     src/lists/count_elements.cu
+    src/lists/drop_list_duplicates.cu
     src/lists/explode.cu
     src/lists/extract.cu
-    src/lists/drop_list_duplicates.cu
+    src/lists/interleave_columns.cu
     src/lists/lists_column_factories.cu
     src/lists/lists_column_view.cu
     src/lists/segmented_sort.cu

cpp/include/cudf/lists/detail/interleave_columns.hpp

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2021, 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/column/column.hpp>
+#include <cudf/table/table_view.hpp>
+
+#include <rmm/cuda_stream_view.hpp>
+
+namespace cudf {
+namespace lists {
+namespace detail {
+
+/**
+ * @brief Returns a single column by interleaving rows of the given table of list elements.
+ *
+ * @code{.pseudo}
+ * s1 = [{0, 1}, {2, 3, 4}, {5}, {}, {6, 7}]
+ * s2 = [{8}, {9}, {}, {10, 11, 12}, {13, 14, 15, 16}]
+ * r = lists::interleave_columns(s1, s2)
+ * r is now [{0, 1}, {8}, {2, 3, 4}, {9}, {5}, {}, {}, {10, 11, 12}, {6, 7}, {13, 14, 15, 16}]
+ * @endcode
+ *
+ * @throws cudf::logic_error if any column of the input table is not a lists columns.
+ * @throws cudf::logic_error if any lists column contains nested typed entry.
+ * @throws cudf::logic_error if all lists columns do not have the same entry type.
+ *
+ * @param input Table containing lists columns to interleave.
+ * @param has_null_mask A boolean flag indicating that the input columns have a null mask.
+ * @param stream CUDA stream used for device memory operations and kernel launches.
+ * @param mr Device memory resource used to allocate the returned column's device memory.
+ * @return The interleaved columns as a single column.
+ */
+std::unique_ptr<column> interleave_columns(
+  table_view const& input,
+  bool has_null_mask,
+  rmm::cuda_stream_view stream,
+  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
+}  // namespace detail
+}  // namespace lists
+}  // namespace cudf