Contents

Column accessor

The column_accessor class provides a read-only access to the column values of the table as contiguous homogeneous array.

Usage example

#include <CL/sycl.hpp>
#include <iostream>

#include "oneapi/dal/table/homogen.hpp"
#include "oneapi/dal/table/column_accessor.hpp"

using namespace oneapi;

int main() {
   sycl::queue queue { sycl::default_selector() };

   constexpr float host_data[] = {
      1.0f, 1.5f, 2.0f,
      2.1f, 3.2f, 3.7f,
      4.0f, 4.9f, 5.0f,
      5.2f, 6.1f, 6.2f
   };

   constexpr std::int64_t row_count = 4;
   constexpr std::int64_t column_count = 3;

   auto shared_data = sycl::malloc_shared<float>(row_count * column_count, queue);
   auto event = queue.memcpy(shared_data, host_data, sizeof(float) * row_count * column_count);
   auto t = dal::homogen_table::wrap(queue, data, row_count, column_count, { event });

   // Accessing whole elements in a first column
   dal::column_accessor<const float> acc { t };

   auto block = acc.pull(queue, 0);
   for(std::int64_t i = 0; i < block.get_count(); i++) {
      std::cout << block[i] << ", ";
   }
   std::cout << std::endl;

   sycl::free(shared_data, queue);
   return 0;
}

Programming interface

All types and functions in this section are declared in the oneapi::dal namespace and be available via inclusion of the oneapi/dal/table/column_accessor.hpp header file.

template<typename T>
class column_accessor
Template Parameters

T – The type of data values in blocks returned by the accessor. Should be const-qualified for read-only access. An accessor supports at least float, double, and std::int32_t.

Constructors

template<typename U = T, std::enable_if_t<std::is_const_v<U>, int> = 0>
column_accessor(const table &table)

Creates a read-only accessor object from the table. Available only for const-qualified T.

column_accessor(const detail::table_builder &builder)

Public Methods

dal::array<data_t> pull(std::int64_t column_index, const range &row_range = {0, -1}) const

Provides access to the column values of the table. The method returns an array that directly points to the memory within the table if it is possible. In that case, the array refers to the memory as to immutable data. Otherwise, the new memory block is allocated, the data from the table rows is converted and copied into this block. In this case, the array refers to the block as to mutable data.

Parameters

  • column_index – The index of the column from which the data is returned by the accessor.

  • row_range – The range of rows that should be read in the column_index block.

Preconditions
row_range are within the range of [0, obj.row_count).
column_index is within the range of [0, obj.column_count).
T *pull(dal::array<data_t> &block, std::int64_t column_index, const range &row_range = {0, -1}) const

Provides access to the column values of the table. The method returns an array that directly points to the memory within the table if it is possible. In that case, the array refers to the memory as to immutable data. Otherwise, the new memory block is allocated, the data from the table rows is converted and copied into this block. In this case, the array refers to the block as to mutable data. The method updates the block array.

Parameters

  • block – The block which memory is reused (if it is possible) to obtain the data from the table. The block memory is reset either when its size is not big enough, or when it contains immutable data, or when direct memory from the table can be used. If the block is reset to use a direct memory pointer from the object, it refers to this pointer as to immutable memory block.

  • column_index – The index of the column from which the data is returned by the accessor.

  • row_range – The range of rows that should be read in the column_index block.

Preconditions
row_range are within the range of [0, obj.row_count).
column_index is within the range of [0, obj.column_count).
template<typename U = T, std::enable_if_t<!std::is_const_v<U>, int> = 0>
void push(const dal::array<data_t> &block, std::int64_t column_index, const range &row_range = {0, -1})

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Row accessor