◆ inclusive_scan_by_key() [1/6]

template<typename DerivedPolicy , typename InputIterator1 , typename InputIterator2 , typename OutputIterator >
__host__ __device__ OutputIterator thrust::inclusive_scan_by_key ( const thrust::detail::execution_policy_base< DerivedPolicy > &  exec,
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.

Results are not deterministic for pseudo-associative operators (e.g., addition of floating-point types). Results for pseudo-associative operators may vary from run to run.

The algorithm's execution is parallelized as determined by exec.

execThe execution policy to use for parallelization.
first1The beginning of the key sequence.
last1The end of the key sequence.
first2The beginning of the input value sequence.
resultThe beginning of the output value sequence.
The end of the output sequence.
Template Parameters
DerivedPolicyThe name of the derived execution policy.
InputIterator1is a model of Input Iterator
InputIterator2is a model of Input Iterator and InputIterator2's value_type is convertible to OutputIterator's value_type.
OutputIteratoris a model of Output Iterator, and if x and y are objects of OutputIterator's value_type, then binary_op(x,y) is defined.
first1 may equal result but the range [first1, last1) and the range [result, result + (last1 - first1)) shall not overlap otherwise.
first2 may equal result but the range [first2, first2 + (last1 - first1) and range [result, result + (last1 - first1)) shall not overlap otherwise.

The following code snippet demonstrates how to use inclusive_scan_by_key using the thrust::host execution policy for parallelization:

#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(thrust::host, keys, keys + 10, data, data); // in-place scan
// data is now {1, 2, 3, 1, 2, 1, 1, 2, 3, 4};
See also