thrust::exclusive_scan_by_key

Defined in thrust/scan.h

template<typename DerivedPolicy, typename InputIterator1, typename InputIterator2, typename OutputIterator> OutputIterator thrust::exclusive_scan_by_key(const thrust::detail::execution_policy_base<DerivedPolicy> &exec, InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, OutputIterator result)

exclusive_scan_by_key computes an exclusive segmented prefix

This version of exclusive_scan_by_key uses the value 0 to initialize the exclusive scan operation.

This version of exclusive_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.

This version of exclusive_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.

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.

Refer to the most general form of exclusive_scan_by_key for additional details.

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

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

#include <thrust/scan.h>
#include <thrust/execution_policy.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};

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

// vals is now {0, 1, 2, 0, 1, 0, 0, 1, 2, 3};