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cudf::column_view Class Reference

A non-owning, immutable view of device data as a column of elements, some of which may be null as indicated by a bitmask. More...

#include <column_view.hpp>

Inheritance diagram for cudf::column_view:
cudf::detail::column_view_base cudf::dictionary_column_view cudf::lists_column_view cudf::strings_column_view cudf::structs_column_view cudf::tdigest::tdigest_column_view

Public Member Functions

 column_view (column_view const &)=default
 Copy constructor.
 
 column_view (column_view &&)=default
 Move constructor.
 
column_viewoperator= (column_view const &)=default
 Copy assignment operator. More...
 
column_viewoperator= (column_view &&)=default
 Move assignment operator. More...
 
 column_view (data_type type, size_type size, void const *data, bitmask_type const *null_mask, size_type null_count, size_type offset=0, std::vector< column_view > const &children={})
 Construct a column_view from pointers to device memory for the elements and bitmask of the column. More...
 
column_view child (size_type child_index) const noexcept
 Returns the specified child. More...
 
size_type num_children () const noexcept
 Returns the number of child columns. More...
 
auto child_begin () const noexcept
 Returns iterator to the beginning of the ordered sequence of child column-views. More...
 
auto child_end () const noexcept
 Returns iterator to the end of the ordered sequence of child column-views. More...
 
template<typename T , CUDF_ENABLE_IF(cudf::is_numeric< T >() or cudf::is_chrono< T >()) >
 column_view (device_span< T const > data)
 Construct a column view from a device_span<T>. More...
 
template<typename T , CUDF_ENABLE_IF(cudf::is_numeric< T >() or cudf::is_chrono< T >()) >
 operator device_span< T const > () const
 Converts a column view into a device span. More...
 
- Public Member Functions inherited from cudf::detail::column_view_base
template<typename T = void, CUDF_ENABLE_IF(std::is_same_v< T, void > or is_rep_layout_compatible< T >()) >
T const * head () const noexcept
 Returns pointer to the base device memory allocation casted to the specified type. More...
 
template<typename T , CUDF_ENABLE_IF(is_rep_layout_compatible< T >()) >
T const * data () const noexcept
 Returns the underlying data casted to the specified type, plus the offset. More...
 
template<typename T , CUDF_ENABLE_IF(is_rep_layout_compatible< T >()) >
T const * begin () const noexcept
 Return first element (accounting for offset) after underlying data is casted to the specified type. More...
 
template<typename T , CUDF_ENABLE_IF(is_rep_layout_compatible< T >()) >
T const * end () const noexcept
 Return one past the last element after underlying data is casted to the specified type. More...
 
size_type size () const noexcept
 Returns the number of elements in the column. More...
 
bool is_empty () const noexcept
 Returns true if size() returns zero, or false otherwise. More...
 
data_type type () const noexcept
 Returns the element data_type More...
 
bool nullable () const noexcept
 Indicates if the column can contain null elements, i.e., if it has an allocated bitmask. More...
 
size_type null_count () const
 Returns the count of null elements. More...
 
size_type null_count (size_type begin, size_type end) const
 Returns the count of null elements in the range [begin, end) More...
 
bool has_nulls () const
 Indicates if the column contains null elements, i.e., null_count() > 0 More...
 
bool has_nulls (size_type begin, size_type end) const
 Indicates if the column contains null elements in the range [begin, end), i.e., null_count(begin, end) > 0 More...
 
bitmask_type const * null_mask () const noexcept
 Returns raw pointer to the underlying bitmask allocation. More...
 
size_type offset () const noexcept
 Returns the index of the first element relative to the base memory allocation, i.e., what is returned from head<T>(). More...
 

Protected Member Functions

void const * get_data () const noexcept override
 Returns pointer to the base device memory allocation. More...
 
- Protected Member Functions inherited from cudf::detail::column_view_base
 column_view_base (column_view_base const &)=default
 Copy constructor.
 
 column_view_base (column_view_base &&)=default
 Move constructor.
 
column_view_baseoperator= (column_view_base const &)=default
 Copy assignment operator. More...
 
column_view_baseoperator= (column_view_base &&)=default
 Move assignment operator. More...
 
 column_view_base (data_type type, size_type size, void const *data, bitmask_type const *null_mask, size_type null_count, size_type offset=0)
 Construct a column_view_base from pointers to device memory for the elements and bitmask of the column. More...
 

Friends

column_view bit_cast (column_view const &input, data_type type)
 Zero-copy cast between types with the same size and compatible underlying representations. More...
 

Additional Inherited Members

- Protected Attributes inherited from cudf::detail::column_view_base
data_type _type {type_id::EMPTY}
 Element type.
 
size_type _size {}
 Number of elements.
 
void const * _data {}
 Pointer to device memory containing elements.
 
bitmask_type const * _null_mask {}
 
size_type _null_count {}
 The number of null elements.
 
size_type _offset {}
 

Detailed Description

A non-owning, immutable view of device data as a column of elements, some of which may be null as indicated by a bitmask.

A column_view can be constructed implicitly from a cudf::column, or may be constructed explicitly from a pointer to pre-existing device memory.

Unless otherwise noted, the memory layout of the column_view's data and bitmask is expected to adhere to the Arrow Physical Memory Layout Specification: https://arrow.apache.org/docs/memory_layout.html

Because column_view is non-owning, no device memory is allocated nor freed when column_view objects are created or destroyed.

To enable zero-copy slicing, a column_view has an offset that indicates the index of the first element in the column relative to the base device memory allocation. By default, offset() is zero.

Definition at line 321 of file column_view.hpp.

Constructor & Destructor Documentation

◆ column_view() [1/2]

cudf::column_view::column_view ( data_type  type,
size_type  size,
void const *  data,
bitmask_type const *  null_mask,
size_type  null_count,
size_type  offset = 0,
std::vector< column_view > const &  children = {} 
)

Construct a column_view from pointers to device memory for the elements and bitmask of the column.

If null_count() is zero, null_mask is optional.

If type is EMPTY, the specified null_count will be ignored and null_count() will always return the same value as size()

Exceptions
cudf::logic_errorif size < 0
cudf::logic_errorif size > 0 but data == nullptr
cudf::logic_errorif type.id() == EMPTY but data != nullptr or null_mask != nullptr
cudf::logic_errorif null_count > 0, but null_mask == nullptr
cudf::logic_errorif offset < 0
Parameters
typeThe element type
sizeThe number of elements
dataPointer to device memory containing the column elements
null_maskPointer to device memory containing the null indicator bitmask
null_countThe number of null elements.
offsetOptional, index of the first element
childrenOptional, depending on the element type, child columns may contain additional data

◆ column_view() [2/2]

template<typename T , CUDF_ENABLE_IF(cudf::is_numeric< T >() or cudf::is_chrono< T >()) >
cudf::column_view::column_view ( device_span< T const >  data)
inline

Construct a column view from a device_span<T>.

Only numeric and chrono types are supported.

Template Parameters
TThe device span type. Must be const and match the column view's type.
Parameters
dataA typed device span containing the column view's data.

Definition at line 428 of file column_view.hpp.

Member Function Documentation

◆ child()

column_view cudf::column_view::child ( size_type  child_index) const
inlinenoexcept

Returns the specified child.

Parameters
child_indexThe index of the desired child
Returns
The requested child column_view

Definition at line 393 of file column_view.hpp.

◆ child_begin()

auto cudf::column_view::child_begin ( ) const
inlinenoexcept

Returns iterator to the beginning of the ordered sequence of child column-views.

Returns
An iterator to a column_view referencing the first child column

Definition at line 410 of file column_view.hpp.

◆ child_end()

auto cudf::column_view::child_end ( ) const
inlinenoexcept

Returns iterator to the end of the ordered sequence of child column-views.

Returns
An iterator to a column_view one past the end of the child columns

Definition at line 417 of file column_view.hpp.

◆ get_data()

void const* cudf::column_view::get_data ( ) const
overrideprotectedvirtualnoexcept

Returns pointer to the base device memory allocation.

The primary purpose of this function is to allow derived classes to override the fundamental properties of memory accesses without needing to change all of the different accessors for the underlying pointer.

Returns
Typed pointer to underlying data

Reimplemented from cudf::detail::column_view_base.

◆ num_children()

size_type cudf::column_view::num_children ( ) const
inlinenoexcept

Returns the number of child columns.

Returns
The number of child columns

Definition at line 403 of file column_view.hpp.

◆ operator device_span< T const >()

template<typename T , CUDF_ENABLE_IF(cudf::is_numeric< T >() or cudf::is_chrono< T >()) >
cudf::column_view::operator device_span< T const > ( ) const
inline

Converts a column view into a device span.

Only numeric and chrono data types are supported. The column view must not be nullable.

Template Parameters
TThe device span type. Must be const and match the column view's type.
Exceptions
cudf::logic_errorif the column view type does not match the span type.
cudf::logic_errorif the column view is nullable.
Returns
A typed device span of the column view's data.

Definition at line 450 of file column_view.hpp.

◆ operator=() [1/2]

column_view& cudf::column_view::operator= ( column_view &&  )
default

Move assignment operator.

Returns
Reference to this object

◆ operator=() [2/2]

column_view& cudf::column_view::operator= ( column_view const &  )
default

Copy assignment operator.

Returns
Reference to this object

Friends And Related Function Documentation

◆ bit_cast

column_view bit_cast ( column_view const &  input,
data_type  type 
)
friend

Zero-copy cast between types with the same size and compatible underlying representations.

This is similar to reinterpret_cast or bit_cast in that it gives a view of the same raw bits as a different type. Unlike reinterpret_cast however, this cast is only allowed on types that have the same width and compatible representations. For example, the way timestamp types are laid out in memory is equivalent to an integer representing a duration since a fixed epoch; bit-casting to the same integer type (INT32 for days, INT64 for others) results in a raw view of the duration count. A FLOAT32 can also be bit-casted into INT32 and treated as an integer value. However, an INT32 column cannot be bit-casted to INT64 as the sizes differ, nor can a string_view column be casted into a numeric type column as their data representations are not compatible.

The validity of the conversion can be checked with cudf::is_bit_castable().

Exceptions
cudf::logic_errorif the specified cast is not possible, i.e., is_bit_castable(input.type(), type) is false.
Parameters
inputThe column_view to cast from
typeThe data_type to cast to
Returns
New column_view wrapping the same data as input but cast to type

The documentation for this class was generated from the following file: