list_device_view.cuh

/*
 * SPDX-FileCopyrightText: Copyright (c) 2020-2025, NVIDIA CORPORATION.
 * SPDX-License-Identifier: Apache-2.0
 */
#pragma once
 
#include <cudf/detail/iterator.cuh>
#include <cudf/lists/lists_column_device_view.cuh>
#include <cudf/types.hpp>
#include <cudf/utilities/type_dispatcher.hpp>
 
#include <cuda_runtime.h>
#include <thrust/iterator/counting_iterator.h>
#include <thrust/iterator/transform_iterator.h>
#include <thrust/pair.h>
 
namespace CUDF_EXPORT cudf {
 
class list_device_view {
  using lists_column_device_view = cudf::detail::lists_column_device_view;
 
 public:
  list_device_view() = default;
 
  __device__ inline list_device_view(lists_column_device_view const& lists_column,
                                     size_type const& row_index)
    : lists_column(lists_column), _row_index(row_index)
  {
    column_device_view const& offsets = lists_column.offsets();
    cudf_assert(row_index >= 0 && row_index < lists_column.size() && row_index < offsets.size() &&
                "row_index out of bounds");
 
    begin_offset = offsets.element<size_type>(row_index + lists_column.offset());
    cudf_assert(begin_offset >= 0 && begin_offset <= lists_column.child().size() &&
                "begin_offset out of bounds.");
    _size = offsets.element<size_type>(row_index + 1 + lists_column.offset()) - begin_offset;
  }
 
  ~list_device_view() = default;
 
  [[nodiscard]] __device__ inline size_type element_offset(size_type idx) const
  {
    cudf_assert(idx >= 0 && idx < size() && "idx out of bounds");
    return begin_offset + idx;
  }
 
  template <typename T>
  __device__ inline T element(size_type idx) const
  {
    return lists_column.child().element<T>(element_offset(idx));
  }
 
  [[nodiscard]] __device__ inline bool is_null(size_type idx) const
  {
    cudf_assert(idx >= 0 && idx < size() && "Index out of bounds.");
    auto element_offset = begin_offset + idx;
    return lists_column.child().is_null(element_offset);
  }
 
  [[nodiscard]] __device__ inline bool is_null() const { return lists_column.is_null(_row_index); }
 
  [[nodiscard]] __device__ inline size_type size() const { return _size; }
 
  [[nodiscard]] __device__ inline size_type row_index() const { return _row_index; }
 
  [[nodiscard]] __device__ inline lists_column_device_view const& get_column() const
  {
    return lists_column;
  }
 
  template <typename T>
  struct pair_accessor;
 
  template <typename T>
  struct pair_rep_accessor;
 
  template <typename T>
  using const_pair_iterator =
    thrust::transform_iterator<pair_accessor<T>, thrust::counting_iterator<cudf::size_type>>;
 
  template <typename T>
  using const_pair_rep_iterator =
    thrust::transform_iterator<pair_rep_accessor<T>, thrust::counting_iterator<cudf::size_type>>;
 
  template <typename T>
  [[nodiscard]] __device__ inline const_pair_iterator<T> pair_begin() const
  {
    return const_pair_iterator<T>{thrust::counting_iterator<size_type>(0), pair_accessor<T>{*this}};
  }
 
  template <typename T>
  [[nodiscard]] __device__ inline const_pair_iterator<T> pair_end() const
  {
    return const_pair_iterator<T>{thrust::counting_iterator<size_type>(size()),
                                  pair_accessor<T>{*this}};
  }
 
  template <typename T>
  [[nodiscard]] __device__ inline const_pair_rep_iterator<T> pair_rep_begin() const
  {
    return const_pair_rep_iterator<T>{thrust::counting_iterator<size_type>(0),
                                      pair_rep_accessor<T>{*this}};
  }
 
  template <typename T>
  [[nodiscard]] __device__ inline const_pair_rep_iterator<T> pair_rep_end() const
  {
    return const_pair_rep_iterator<T>{thrust::counting_iterator<size_type>(size()),
                                      pair_rep_accessor<T>{*this}};
  }
 
 private:
  lists_column_device_view const& lists_column;
  size_type _row_index{};  // Row index in the Lists column vector.
  size_type _size{};       // Number of elements in *this* list row.
 
  size_type begin_offset;  // Offset in list_column_device_view where this list begins.
 
  template <typename T>
  struct pair_accessor {
    list_device_view const& list;  
 
    explicit CUDF_HOST_DEVICE inline pair_accessor(list_device_view const& _list) : list{_list} {}
 
    __device__ inline thrust::pair<T, bool> operator()(cudf::size_type i) const
    {
      return {list.element<T>(i), !list.is_null(i)};
    }
  };
 
  template <typename T>
  struct pair_rep_accessor {
    list_device_view const& list;  
 
    using rep_type = device_storage_type_t<T>;  
 
    explicit CUDF_HOST_DEVICE inline pair_rep_accessor(list_device_view const& _list) : list{_list}
    {
    }
 
    __device__ inline thrust::pair<rep_type, bool> operator()(cudf::size_type i) const
    {
      return {get_rep<T>(i), !list.is_null(i)};
    }
 
   private:
    template <typename R>
    __device__ inline rep_type get_rep(cudf::size_type i) const
      requires(std::is_same_v<R, rep_type>)
    {
      return list.element<R>(i);
    }
 
    template <typename R>
    __device__ inline rep_type get_rep(cudf::size_type i) const
      requires(not std::is_same_v<R, rep_type>)
    {
      return list.element<R>(i).value();
    }
  };
};
 
struct list_size_functor {
  detail::lists_column_device_view const d_column;  
  CUDF_HOST_DEVICE inline list_size_functor(detail::lists_column_device_view const& d_col)
    : d_column(d_col)
  {
  }
  __device__ inline size_type operator()(size_type idx)
  {
    if (d_column.is_null(idx)) return size_type{0};
    return d_column.offset_at(idx + 1) - d_column.offset_at(idx);
  }
};
 
CUDF_HOST_DEVICE auto inline make_list_size_iterator(detail::lists_column_device_view const& c)
{
  return detail::make_counting_transform_iterator(0, list_size_functor{c});
}
 
}  // namespace CUDF_EXPORT cudf