Defined in header <numeric>  

template< class InputIt, class OutputIt, class T, class BinaryOperation, class UnaryOperation> OutputIt transform_exclusive_scan( InputIt first, InputIt last, OutputIt d_first, T init, BinaryOperation binary_op, UnaryOperation unary_op);  (1)  (since C++17) 
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T, class BinaryOperation, class UnaryOperation > ForwardIt2 transform_exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first, T init, BinaryOperation binary_op, UnaryOperation unary_op );  (2)  (since C++17) 
Transforms each element in the range [first, last)
with unary_op
, then computes an exclusive prefix sum operation using binary_op
over the resulting range, with init
as the initial value, and writes the results to the range beginning at d_first
. "exclusive" means that the ith input element is not included in the ith sum.
Formally, assigns through each iterator i
in [d_first, d_first + (last  first)) the value of the generalized noncommutative sum of init, unary_op(*j)...
for every j
in [first, first + (i  d_first)) over binary_op
,
where generalized noncommutative sum GNSUM(op, a
1, ..., a
N) is defined as follows:
In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if binary_op
is not associative.
Overload (2) is executed according to policy
, and does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
is true.
unary_op
and binary_op
shall not invalidate iterators (including the end iterators) or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first + (last  first)). Otherwise, the behavior is undefined.
first, last    the range of elements to sum 
d_first    the beginning of the destination range, may be equal to first 
policy    the execution policy to use. See execution policy for details. 
init    the initial value 
unary_op    unary FunctionObject that will be applied to each element of the input range. The return type must be acceptable as input to binary_op . 
binary_op    binary FunctionObject that will be applied in to the result of unary_op , the results of other binary_op , and init . 
Type requirements  
InputIt must meet the requirements of LegacyInputIterator. 

OutputIt must meet the requirements of LegacyOutputIterator. 

ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator. 

T must meet the requirements of MoveConstructible. All of binary_op(init, unary_op(*first)) , binary_op(init, init) , and binary_op(unary_op(*first), unary_op(*first)) must be convertible to T . 
Iterator to the element past the last element written.
O(last  first) applications of each of binary_op
and unary_op
.
The overload with a template parameter named ExecutionPolicy
reports errors as follows:
ExecutionPolicy
is one of the standard policies, std::terminate
is called. For any other ExecutionPolicy
, the behavior is implementationdefined. std::bad_alloc
is thrown. unary_op
is not applied to init
.
#include <functional> #include <iostream> #include <iterator> #include <numeric> #include <vector> int times_10(int x) { return x * 10; } int main() { std::vector data {3, 1, 4, 1, 5, 9, 2, 6}; std::cout << "10 times exclusive sum: "; std::transform_exclusive_scan(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " "), 0, std::plus<int>{}, times_10); std::cout << "\n10 times inclusive sum: "; std::transform_inclusive_scan(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " "), std::plus<int>{}, times_10); }
Output:
10 times exclusive sum: 0 30 40 80 90 140 230 250 10 times inclusive sum: 30 40 80 90 140 230 250 310
computes the partial sum of a range of elements (function template) 

(C++17)  similar to std::partial_sum , excludes the ith input element from the ith sum (function template) 
(C++17)  applies a functor, then calculates inclusive scan (function template) 
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