Copying

Modules
	Concatenating
	Gathering
	Scattering
	Slicing
	Splitting
	Shifting

Files
file	copying.hpp
	Column APIs for gather, scatter, split, slice, etc.

Enumerations
enum class	cudf::out_of_bounds_policy : bool { cudf::NULLIFY , cudf::DONT_CHECK }
	Policy to account for possible out-of-bounds indices. More...
enum class	cudf::mask_allocation_policy : int32_t { cudf::NEVER , cudf::RETAIN , cudf::ALWAYS }
	Indicates when to allocate a mask, based on an existing mask. More...
enum class	cudf::sample_with_replacement : bool { cudf::FALSE , cudf::TRUE }
	Indicates whether a row can be sampled more than once. More...

Functions
std::unique_ptr< table >	cudf::reverse (table_view const &source_table, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Reverses the rows within a table. More...
std::unique_ptr< column >	cudf::reverse (column_view const &source_column, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Reverses the elements of a column. More...
std::unique_ptr< column >	cudf::empty_like (column_view const &input)
	Initializes and returns an empty column of the same type as the input. More...
std::unique_ptr< column >	cudf::empty_like (scalar const &input)
	Initializes and returns an empty column of the same type as the input. More...
std::unique_ptr< column >	cudf::allocate_like (column_view const &input, mask_allocation_policy mask_alloc=mask_allocation_policy::RETAIN, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Creates an uninitialized new column of the same size and type as the input. More...
std::unique_ptr< column >	cudf::allocate_like (column_view const &input, size_type size, mask_allocation_policy mask_alloc=mask_allocation_policy::RETAIN, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Creates an uninitialized new column of the specified size and same type as the input. More...
std::unique_ptr< table >	cudf::empty_like (table_view const &input_table)
	Creates a table of empty columns with the same types as the input_table More...
void	cudf::copy_range_in_place (column_view const &source, mutable_column_view &target, size_type source_begin, size_type source_end, size_type target_begin, rmm::cuda_stream_view stream=cudf::get_default_stream())
	Copies a range of elements in-place from one column to another. More...
std::unique_ptr< column >	cudf::copy_range (column_view const &source, column_view const &target, size_type source_begin, size_type source_end, size_type target_begin, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Copies a range of elements out-of-place from one column to another. More...
std::unique_ptr< column >	cudf::copy_if_else (column_view const &lhs, column_view const &rhs, column_view const &boolean_mask, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask. More...
std::unique_ptr< column >	cudf::copy_if_else (scalar const &lhs, column_view const &rhs, column_view const &boolean_mask, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask. More...
std::unique_ptr< column >	cudf::copy_if_else (column_view const &lhs, scalar const &rhs, column_view const &boolean_mask, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask. More...
std::unique_ptr< column >	cudf::copy_if_else (scalar const &lhs, scalar const &rhs, column_view const &boolean_mask, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask. More...
std::unique_ptr< scalar >	cudf::get_element (column_view const &input, size_type index, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Get the element at specified index from a column. More...
std::unique_ptr< table >	cudf::sample (table_view const &input, size_type const n, sample_with_replacement replacement=sample_with_replacement::FALSE, int64_t const seed=0, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Gather n samples from given input randomly. More...
bool	cudf::has_nonempty_nulls (column_view const &input, rmm::cuda_stream_view stream=cudf::get_default_stream())
	Checks if a column or its descendants have non-empty null rows. More...
bool	cudf::may_have_nonempty_nulls (column_view const &input)
	Approximates if a column or its descendants may have non-empty null elements. More...
std::unique_ptr< column >	cudf::purge_nonempty_nulls (column_view const &input, rmm::cuda_stream_view stream=cudf::get_default_stream(), rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Copy input into output while purging any non-empty null rows in the column or its descendants. More...

Detailed Description

Enumeration Type Documentation

mask_allocation_policy

enum cudf::mask_allocation_policy : int32_t

strong

Indicates when to allocate a mask, based on an existing mask.

Enumerator
NEVER	Do not allocate a null mask, regardless of input.
RETAIN	Allocate a null mask if the input contains one.
ALWAYS	Allocate a null mask, regardless of input.

Definition at line 226 of file copying.hpp.

out_of_bounds_policy

enum cudf::out_of_bounds_policy : bool

strong

Policy to account for possible out-of-bounds indices.

NULLIFY means to nullify output values corresponding to out-of-bounds gather_map values. DONT_CHECK means do not check whether the indices are out-of-bounds, for better performance.

Enumerator
NULLIFY	Output values corresponding to out-of-bounds indices are null.
DONT_CHECK	No bounds checking is performed, better performance.

Definition at line 48 of file copying.hpp.

sample_with_replacement

enum cudf::sample_with_replacement : bool

strong

Indicates whether a row can be sampled more than once.

Enumerator
FALSE	A row can be sampled only once.
TRUE	A row can be sampled more than once.

Definition at line 812 of file copying.hpp.

Function Documentation

allocate_like() [1/2]

std::unique_ptr<column> cudf::allocate_like	(	column_view const &	input,
		mask_allocation_policy	mask_alloc = mask_allocation_policy::RETAIN,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Creates an uninitialized new column of the same size and type as the input.

Supports only fixed-width types.

If the mask_alloc allocates a validity mask that mask is also uninitialized and the validity bits and the null count should be set by the caller.

Parameters

input	Immutable view of input column to emulate
mask_alloc	Optional, Policy for allocating null mask. Defaults to RETAIN
mr	Device memory resource used to allocate the returned column's device memory
stream	CUDA stream used for device memory operations and kernel launches

Returns

A column with sufficient uninitialized capacity to hold the same number of elements as input of the same type as input.type()

allocate_like() [2/2]

std::unique_ptr<column> cudf::allocate_like	(	column_view const &	input,
		size_type	size,
		mask_allocation_policy	mask_alloc = mask_allocation_policy::RETAIN,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Creates an uninitialized new column of the specified size and same type as the input.

Supports only fixed-width types.

If the mask_alloc allocates a validity mask that mask is also uninitialized and the validity bits and the null count should be set by the caller.

Parameters

input	Immutable view of input column to emulate
size	The desired number of elements that the new column should have capacity for
mask_alloc	Optional, Policy for allocating null mask. Defaults to RETAIN
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

A column with sufficient uninitialized capacity to hold the specified number of elements as input of the same type as input.type()

copy_if_else() [1/4]

std::unique_ptr<column> cudf::copy_if_else	(	column_view const &	lhs,
		column_view const &	rhs,
		column_view const &	boolean_mask,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask.

Selects each element i in the output column from either rhs or lhs using the following rule: output[i] = (boolean_mask.valid(i) and boolean_mask[i]) ? lhs[i] : rhs[i]

Exceptions

cudf::data_type_error	if lhs and rhs are not of the same type
std::invalid_argument	if lhs and rhs are not of the same length
cudf::data_type_error	if boolean mask is not of type bool
std::invalid_argument	if boolean mask is not of the same length as lhs and rhs

Parameters

lhs	left-hand column_view
rhs	right-hand column_view
boolean_mask	column of type_id::BOOL8 representing "left (true) / right (false)" boolean for each element. Null element represents false.
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

new column with the selected elements

copy_if_else() [2/4]

std::unique_ptr<column> cudf::copy_if_else	(	column_view const &	lhs,
		scalar const &	rhs,
		column_view const &	boolean_mask,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask.

Selects each element i in the output column from either rhs or lhs using the following rule: output[i] = (boolean_mask.valid(i) and boolean_mask[i]) ? lhs[i] : rhs

Exceptions

cudf::data_type_error	if lhs and rhs are not of the same type
cudf::data_type_error	if boolean mask is not of type bool
std::invalid_argument	if boolean mask is not of the same length as lhs and rhs

Parameters

lhs	left-hand column_view
rhs	right-hand scalar
boolean_mask	column of type_id::BOOL8 representing "left (true) / right (false)" boolean for each element. Null element represents false.
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

new column with the selected elements

copy_if_else() [3/4]

std::unique_ptr<column> cudf::copy_if_else	(	scalar const &	lhs,
		column_view const &	rhs,
		column_view const &	boolean_mask,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask.

Selects each element i in the output column from either rhs or lhs using the following rule: output[i] = (boolean_mask.valid(i) and boolean_mask[i]) ? lhs : rhs[i]

Exceptions

cudf::data_type_error	if lhs and rhs are not of the same type
cudf::data_type_error	if boolean mask is not of type bool
std::invalid_argument	if boolean mask is not of the same length as lhs and rhs

Parameters

lhs	left-hand scalar
rhs	right-hand column_view
boolean_mask	column of type_id::BOOL8 representing "left (true) / right (false)" boolean for each element. Null element represents false.
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

new column with the selected elements

copy_if_else() [4/4]

std::unique_ptr<column> cudf::copy_if_else	(	scalar const &	lhs,
		scalar const &	rhs,
		column_view const &	boolean_mask,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Returns a new column, where each element is selected from either lhs or rhs based on the value of the corresponding element in boolean_mask.

Selects each element i in the output column from either rhs or lhs using the following rule: output[i] = (boolean_mask.valid(i) and boolean_mask[i]) ? lhs : rhs

Exceptions

cudf::logic_error

if boolean mask is not of type bool

Parameters

lhs	left-hand scalar
rhs	right-hand scalar
boolean_mask	column of type_id::BOOL8 representing "left (true) / right (false)" boolean for each element. null element represents false.
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

new column with the selected elements

copy_range()

std::unique_ptr<column> cudf::copy_range	(	column_view const &	source,
		column_view const &	target,
		size_type	source_begin,
		size_type	source_end,
		size_type	target_begin,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Copies a range of elements out-of-place from one column to another.

Creates a new column as if an in-place copy was performed into target. A copy of target is created first and then the elements indicated by the indices [target_begin, target_begin + N) were copied from the elements indicated by the indices [source_begin, source_end) of source (where N = (source_end - source_begin)). Elements outside the range are copied from target into the returned new column target.

If source and target refer to the same elements and the ranges overlap, the behavior is undefined.

A range is considered invalid if:

• Either the begin or end indices are out of bounds for the corresponding column
• Begin is greater than end for source or target
• The size of the source range would overflow the target column starting at target_begin

Exceptions

std::out_of_range	for any invalid range.
cudf::data_type_error	if target and source have different types.

Parameters

source	The column to copy from inside the range
target	The column to copy from outside the range
source_begin	The starting index of the source range (inclusive)
source_end	The index of the last element in the source range (exclusive)
target_begin	The starting index of the target range (inclusive)
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

The result target column

copy_range_in_place()

void cudf::copy_range_in_place	(	column_view const &	source,
		mutable_column_view &	target,
		size_type	source_begin,
		size_type	source_end,
		size_type	target_begin,
		rmm::cuda_stream_view	stream = cudf::get_default_stream()
	)

Copies a range of elements in-place from one column to another.

Overwrites the range of elements in target indicated by the indices [target_begin, target_begin + N) with the elements from source indicated by the indices [source_begin, source_end) (where N = (source_end - source_begin)). Use the out-of-place copy function returning std::unique_ptr<column> for uses cases requiring memory reallocation. For example for strings columns and other variable-width types.

If source and target refer to the same elements and the ranges overlap, the behavior is undefined.

Exceptions

cudf::data_type_error	if memory reallocation is required (e.g. for variable width types).
std::out_of_range	for invalid range (if source_begin > source_end, source_begin < 0, source_begin >= source.size(), source_end > source.size(), target_begin < 0, target_begin >= target.size(), or target_begin + (source_end - source_begin) > target.size()).
cudf::data_type_error	if target and source have different types.
std::invalid_argument	if source has null values and target is not nullable.

Parameters

source	The column to copy from
target	The preallocated column to copy into
source_begin	The starting index of the source range (inclusive)
source_end	The index of the last element in the source range (exclusive)
target_begin	The starting index of the target range (inclusive)
stream	CUDA stream used for device memory operations and kernel launches

empty_like() [1/3]

std::unique_ptr<column> cudf::empty_like

(

column_view const &

input

)

Initializes and returns an empty column of the same type as the input.

Parameters

[in]

input

Immutable view of input column to emulate

Returns

An empty column of same type as input

empty_like() [2/3]

std::unique_ptr<column> cudf::empty_like

(

scalar const &

input

)

Initializes and returns an empty column of the same type as the input.

Parameters

[in]

input

Scalar to emulate

Returns

An empty column of same type as input

empty_like() [3/3]

std::unique_ptr<table> cudf::empty_like

(

table_view const &

input_table

)

Creates a table of empty columns with the same types as the input_table

Creates the cudf::column objects, but does not allocate any underlying device memory for the column's data or bitmask.

Parameters

[in]

input_table

Immutable view of input table to emulate

Returns

A table of empty columns with the same types as the columns in input_table

get_element()

std::unique_ptr<scalar> cudf::get_element	(	column_view const &	input,
		size_type	index,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Get the element at specified index from a column.

Warning

This function is expensive (invokes a kernel launch). So, it is not recommended to be used in performance sensitive code or inside a loop.

Exceptions

std::out_of_range

if index is not within the range [0, input.size())

Parameters

input	Column view to get the element from
index	Index into input to get the element at
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned scalar's device memory

Returns

Scalar containing the single value

has_nonempty_nulls()

bool cudf::has_nonempty_nulls	(	column_view const &	input,
		rmm::cuda_stream_view	stream = cudf::get_default_stream()
	)

Checks if a column or its descendants have non-empty null rows.

Note

This function is exact. If it returns true, there exists one or more non-empty null elements.

A LIST or STRING column might have non-empty rows that are marked as null. A STRUCT OR LIST column might have child columns that have non-empty null rows. Other types of columns are deemed incapable of having non-empty null rows. E.g. Fixed width columns have no concept of an "empty" row.

Parameters

input	The column which is (and whose descendants are) to be checked for non-empty null rows.
stream	CUDA stream used for device memory operations and kernel launches

Returns

true If either the column or its descendants have non-empty null rows

false If neither the column or its descendants have non-empty null rows

may_have_nonempty_nulls()

bool cudf::may_have_nonempty_nulls

(

column_view const &

input

)

Approximates if a column or its descendants may have non-empty null elements.

Note

This function is approximate.

• true: Non-empty null elements could exist
• false: Non-empty null elements definitely do not exist

False positives are possible, but false negatives are not.

Compared to the exact has_nonempty_nulls() function, this function is typically more efficient.

Complexity:

• Best case: O(count_descendants(input))
• Worst case: O(count_descendants(input)) * m, where m is the number of rows in the largest descendant

Parameters

input

The column which is (and whose descendants are) to be checked for non-empty null rows

Returns

true If either the column or its descendants have null rows

false If neither the column nor its descendants have null rows

purge_nonempty_nulls()

std::unique_ptr<column> cudf::purge_nonempty_nulls	(	column_view const &	input,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Copy input into output while purging any non-empty null rows in the column or its descendants.

If the input column is not of compound type (LIST/STRING/STRUCT/DICTIONARY), the output will be the same as input.

The purge operation only applies directly to LIST and STRING columns, but it applies indirectly to STRUCT/DICTIONARY columns as well, since these columns may have child columns that are LIST or STRING.

Examples:

auto const lists   = lists_column_wrapper<int32_t>{ {0,1}, {2,3}, {4,5} }.release();
cudf::detail::set_null_mask(lists->null_mask(), 1, 2, false);
 
lists[1] is now null, but the lists child column still stores `{2,3}`.
The lists column contents will be:
  Validity: 101
  Offsets:  [0, 2, 4, 6]
  Child:    [0, 1, 2, 3, 4, 5]
 
After purging the contents of the list's null rows, the column's contents will be:
  Validity: 101
  Offsets:  [0, 2, 2, 4]
  Child:    [0, 1, 4, 5]

auto const strings = strings_column_wrapper{ "AB", "CD", "EF" }.release();
cudf::detail::set_null_mask(strings->null_mask(), 1, 2, false);
 
strings[1] is now null, but the strings column still stores `"CD"`.
The lists column contents will be:
  Validity: 101
  Offsets:  [0, 2, 4, 6]
  Child:    [A, B, C, D, E, F]
 
After purging the contents of the list's null rows, the column's contents
will be:
  Validity: 101
  Offsets:  [0, 2, 2, 4]
  Child:    [A, B, E, F]

auto const lists   = lists_column_wrapper<int32_t>{ {0,1}, {2,3}, {4,5} };
auto const structs = structs_column_wrapper{ {lists}, null_at(1) };
 
structs[1].child is now null, but the lists column still stores `{2,3}`.
The lists column contents will be:
  Validity: 101
  Offsets:  [0, 2, 4, 6]
  Child:    [0, 1, 2, 3, 4, 5]
 
After purging the contents of the list's null rows, the column's contents
will be:
  Validity: 101
  Offsets:  [0, 2, 2, 4]
  Child:    [0, 1, 4, 5]

Parameters

input	The column whose null rows are to be checked and purged
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned column's device memory

Returns

A new column with equivalent contents to input, but with null rows purged

reverse() [1/2]

std::unique_ptr<column> cudf::reverse	(	column_view const &	source_column,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Reverses the elements of a column.

Creates a new column that is the reverse of source_column. Example:

source = [4,5,6]
return = [6,5,4]

Parameters

source_column	Column that will be reversed
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned table's device memory

Returns

Reversed column

reverse() [2/2]

std::unique_ptr<table> cudf::reverse	(	table_view const &	source_table,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Reverses the rows within a table.

Creates a new table that is the reverse of source_table. Example:

source = [[4,5,6], [7,8,9], [10,11,12]]
return = [[6,5,4], [9,8,7], [12,11,10]]

Parameters

source_table	Table that will be reversed
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned table's device memory

Returns

Reversed table

sample()

std::unique_ptr<table> cudf::sample	(	table_view const &	input,
		size_type const	n,
		sample_with_replacement	replacement = sample_with_replacement::FALSE,
		int64_t const	seed = 0,
		rmm::cuda_stream_view	stream = cudf::get_default_stream(),
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Gather n samples from given input randomly.

Example:
input: {col1: {1, 2, 3, 4, 5}, col2: {6, 7, 8, 9, 10}}
n: 3
replacement: false
 
output:       {col1: {3, 1, 4}, col2: {8, 6, 9}}
 
replacement: true
 
output:       {col1: {3, 1, 1}, col2: {8, 6, 6}}

Exceptions

cudf::logic_error	if n > input.num_rows() and replacement == FALSE.
cudf::logic_error	if n < 0.

Parameters

input	View of a table to sample
n	non-negative number of samples expected from input
replacement	Allow or disallow sampling of the same row more than once
seed	Seed value to initiate random number generator
stream	CUDA stream used for device memory operations and kernel launches
mr	Device memory resource used to allocate the returned table's device memory

Returns

Table containing samples from input