Column Accessor¶
The column_accessor class provides read-only access to the column values
of the table as contiguous
homogeneous array.
Usage Example¶
#include <sycl/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, shared_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 available via the 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, andstd::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_indexblock.
- 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_indexblock.
- Preconditions
- row_range are within the range of [0, obj.row_count).column_index is within the range of [0, obj.column_count).