std::transform_exclusive_scan (3) - Linux Manuals

std::transform_exclusive_scan: std::transform_exclusive_scan


std::transform_exclusive_scan - std::transform_exclusive_scan


Defined in header <numeric>
template< class InputIt, class OutputIt, class T,
class BinaryOperation, class UnaryOperation> (1) (since C++17)
OutputIt transform_exclusive_scan( InputIt first, InputIt last, OutputIt d_first, T init,
BinaryOperation binary_op, UnaryOperation unary_op);
template< class ExecutionPolicy,
class ForwardIt1, class ForwardIt2,
class T, class BinaryOperation, class UnaryOperation >
ForwardIt2 transform_exclusive_scan( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt1 first, ForwardIt1 last,
ForwardIt2 d_first, T init,
BinaryOperation binary_op, UnaryOperation unary_op );

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 i-th input element is not included in the i-th 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:

* if N=1, a
* if N > 1, op(GNSUM(op, a
  1, ..., a
  K), GNSUM(op, a
  M, ..., a
  N)) for any K where 1 < K+1 = M ≤ N

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.

Return value

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:

* If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard_policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.


unary_op is not applied to init.


// Run this code

  #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);



  10 times exclusive sum: 0 30 40 80 90 140 230 250
  10 times inclusive sum: 30 40 80 90 140 230 250 310

See also

                         computes the partial sum of a range of elements
partial_sum (function template)

exclusive_scan similar to std::partial_sum, excludes the ith input element from the ith sum
                         (function template)

transform_inclusive_scan applies a functor, then calculates inclusive scan
                         (function template)