Template Function thrust::exclusive_scan_by_key(InputIterator1, InputIterator1, InputIterator2, OutputIterator, T, BinaryPredicate, AssociativeOperator)

Function Documentation

template<typename InputIterator1, typename InputIterator2, typename OutputIterator, typename T, typename BinaryPredicate, typename AssociativeOperator>
OutputIterator thrust::exclusive_scan_by_key(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, OutputIterator result, T init, BinaryPredicate binary_pred, AssociativeOperator binary_op)

exclusive_scan_by_key computes an exclusive key-value or ‘segmented’ prefix sum operation. The term ‘exclusive’ means that each result does not include the corresponding input operand in the partial sum. The term ‘segmented’ means that the partial sums are broken into distinct segments. In other words, within each segment a separate exclusive scan operation is computed. Refer to the code sample below for example usage.

This version of exclusive_scan_by_key uses the value init to initialize the exclusive scan operation.

This version of exclusive_scan_by_key uses the binary predicate binary_pred to compare adjacent keys. Specifically, consecutive iterators i and i+1 in the range [first1, last1) belong to the same segment if binary_pred(*i, *(i+1)) is true, and belong to different segments otherwise.

This version of exclusive_scan_by_key uses the associative operator binary_op to perform the prefix sum. When the input and output sequences are the same, the scan is performed in-place.

The following code snippet demonstrates how to use

exclusive_scan_by_key
Return

The end of the output sequence.

Pre

first1 may equal result but the range [first1, last1) and the range [result, result + (last1 - first1)) shall not overlap otherwise.

Pre

first2 may equal result but the range [first2, first2 + (last1 - first1) and range [result, result + (last1 - first1)) shall not overlap otherwise.

Parameters

  • first1: The beginning of the key sequence.

  • last1: The end of the key sequence.

  • first2: The beginning of the input value sequence.

  • result: The beginning of the output value sequence.

  • init: The initial of the exclusive sum value.

  • binary_pred: The binary predicate used to determine equality of keys.

  • binary_op: The associatve operator used to ‘sum’ values.

Template Parameters

  • InputIterator1: is a model of Input Iterator

  • InputIterator2: is a model of Input Iterator and InputIterator2's value_type is convertible to OutputIterator's value_type.

  • OutputIterator: is a model of Output Iterator, and if x and y are objects of OutputIterator's value_type, then binary_op(x,y) is defined.

  • T: is convertible to OutputIterator's value_type.

  • BinaryPredicate: is a model of Binary Predicate.

  • AssociativeOperator: is a model of Binary Function and AssociativeOperator's result_type is convertible to OutputIterator's value_type.

#include <thrust/scan.h>
#include <thrust/functional.h>

int keys[10] = {0, 0, 0, 1, 1, 2, 3, 3, 3, 3};
int vals[10] = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1};

int init = 5;

thrust::equal_to<int> binary_pred;
thrust::plus<int>     binary_op;

thrust::exclusive_scan_by_key(key, key + 10, vals, vals, init, binary_pred, binary_op); // in-place scan

// vals is now {5, 6, 7, 5, 6, 5, 5, 6, 7, 8};

See

exclusive_scan

See

inclusive_scan_by_key