Template Function thrust::inclusive_scan_by_key(InputIterator1, InputIterator1, InputIterator2, OutputIterator)

Function Documentation

template<typename InputIterator1, typename InputIterator2, typename OutputIterator>
OutputIterator thrust::inclusive_scan_by_key(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, OutputIterator result)

inclusive_scan_by_key computes an inclusive key-value or ‘segmented’ prefix sum operation. The term ‘inclusive’ means that each result includes 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 inclusive scan operation is computed. Refer to the code sample below for example usage.

This version of inclusive_scan_by_key assumes equal_to as the binary predicate used to compare adjacent keys. Specifically, consecutive iterators i and i+1 in the range [first1, last1) belong to the same segment if *i == *(i+1), and belong to different segments otherwise.

This version of inclusive_scan_by_key assumes plus as the associative operator used 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

inclusive_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.

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.

#include <thrust/scan.h>

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

thrust::inclusive_scan_by_key(keys, keys + 10, vals, vals); // in-place scan

// data is now {1, 2, 3, 1, 2, 1, 1, 2, 3, 4};

See

inclusive_scan

See

exclusive_scan_by_key