std::transform_exclusive_scan

The generalized noncommutative sum of a sequence of elements over a binary operation binary_op is defined as follows:

• If the sequence only has one element, the sum is the value of the element.
• Otherwise, performs the following operations in order:

1. Selects any two adjacent elements elem1 and elem2 from the sequence.
2. Calculates binary_op(elem1, elem2) and replaces the two elements in the sequence with the result.
3. Repeats steps 1 and 2 until there is only one element in the sequence.

The result is non-deterministic if the binary_op is not associative (such as floating-point addition).

If any of the following values is not convertible to T, the program is ill-formed:

• binary_op(init, init)
• binary_op(init, unary_op(*first))
• binary_op(unary_op( *first), unary_op( *first) )

If any of the following conditions is satisfied, the behavior is undefined:

• T is not MoveConstructible.
• unary_op or binary_op modifies any element of [first, last)
• unary_op or binary_op invalidates any iterator or subrange of [first, last]

Parameters

Return value

Iterator to the element past the last element written.

Complexity

Given \(\scriptsize N\) N as std::distance(first, last)

Exceptions

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
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Notes

unary_op is never applied to init.

Example

#include <functional>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
 
int main()
{
    std::vector data{3, 1, 4, 1, 5, 9, 2, 6};
 
    auto times_10 = [](int x) { return x * 10; };
 
    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);
    std::cout << '\n';
}

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