Reduction

Files
file	reduction.hpp

Enumerations
enum	cudf::scan_type : bool { INCLUSIVE, EXCLUSIVE }
	Enum to describe scan operation type.

Functions
std::unique_ptr< scalar >	cudf::reduce (column_view const &col, std::unique_ptr< aggregation > const &agg, data_type output_dtype, rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Computes the reduction of the values in all rows of a column. More...
std::unique_ptr< column >	cudf::scan (const column_view &input, std::unique_ptr< aggregation > const &agg, scan_type inclusive, null_policy null_handling=null_policy::EXCLUDE, rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Computes the scan of a column. More...
std::pair< std::unique_ptr< scalar >, std::unique_ptr< scalar > >	cudf::minmax (column_view const &col, rmm::mr::device_memory_resource *mr=rmm::mr::get_current_device_resource())
	Determines the minimum and maximum values of a column. More...

Detailed Description

Function Documentation

minmax()

std::pair<std::unique_ptr<scalar>, std::unique_ptr<scalar> > cudf::minmax	(	column_view const &	col,
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Determines the minimum and maximum values of a column.

Parameters

col	column to compute minmax
mr	Device memory resource used to allocate the returned column's device memory

Returns

A std::pair of scalars with the first scalar being the minimum value and the second scalar being the maximum value of the input column.

reduce()

std::unique_ptr<scalar> cudf::reduce	(	column_view const &	col,
		std::unique_ptr< aggregation > const &	agg,
		data_type	output_dtype,
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Computes the reduction of the values in all rows of a column.

This function does not detect overflows in reductions. Using a higher precision data_type may prevent overflow. Only min and max ops are supported for reduction of non-arithmetic types (timestamp, string...). The null values are skipped for the operation. If the column is empty, the member is_valid() of the output scalar will contain false.

Exceptions

cudf::logic_error	if reduction is called for non-arithmetic output type and operator other than min and max.
cudf::logic_error	if input column data type is not convertible to output data type.
cudf::logic_error	if min or max reduction is called and the output type does not match the input column data type.

If the input column has arithmetic type, output_dtype can be any arithmetic type. For mean, var and std ops, a floating point output type must be specified. If the input column has non-arithmetic type eg.(timestamp, string...), the same type must be specified.

If the reduction fails, the member is_valid of the output scalar will contain false.

Parameters

col	Input column view
agg	Aggregation operator applied by the reduction
output_dtype	The computation and output precision.
mr	Device memory resource used to allocate the returned scalar's device memory

Returns

Output scalar with reduce result.

scan()

std::unique_ptr<column> cudf::scan	(	const column_view &	input,
		std::unique_ptr< aggregation > const &	agg,
		scan_type	inclusive,
		null_policy	null_handling = null_policy::EXCLUDE,
		rmm::mr::device_memory_resource *	mr = rmm::mr::get_current_device_resource()
	)

Computes the scan of a column.

The null values are skipped for the operation, and if an input element at i is null, then the output element at i will also be null.

Exceptions

cudf::logic_error

if column datatype is not numeric type.

Parameters

[in]	input	The input column view for the scan
[in]	agg	unique_ptr to aggregation operator applied by the scan
[in]	inclusive	The flag for applying an inclusive scan if scan_type::INCLUSIVE, an exclusive scan if scan_type::EXCLUSIVE.
[in]	null_handling	Exclude null values when computing the result if null_policy::EXCLUDE. Include nulls if null_policy::INCLUDE. Any operation with a null results in a null.
[in]	mr	Device memory resource used to allocate the returned scalar's device memory

Returns

unique pointer to new output column