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std::transform_inclusive_scan

From cppreference.com
< cpp‎ | algorithm
 
 
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transform_inclusive_scan
(C++17)

Operations on uninitialized memory
 
Defined in header <numeric>
(1)
template< class InputIt, class OutputIt,

          class BinaryOperation, class UnaryOperation >
OutputIt transform_inclusive_scan( InputIt first, InputIt last,
                                   OutputIt d_first,
                                   BinaryOperation binary_op,

                                   UnaryOperation unary_op );
(since C++17)
(until C++20)
template< class InputIt, class OutputIt,

          class BinaryOperation, class UnaryOperation >
constexpr OutputIt transform_inclusive_scan( InputIt first, InputIt last,
                                             OutputIt d_first,
                                             BinaryOperation binary_op,

                                             UnaryOperation unary_op );
(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,

          class BinaryOperation, class UnaryOperation >
ForwardIt2 transform_inclusive_scan( ExecutionPolicy&& policy,
                                     ForwardIt1 first, ForwardIt1 last,
                                     ForwardIt2 d_first,
                                     BinaryOperation binary_op,

                                     UnaryOperation unary_op );
(2) (since C++17)
(3)
template< class InputIt, class OutputIt,

          class BinaryOperation, class UnaryOperation, class T >
OutputIt transform_inclusive_scan( InputIt first, InputIt last,
                                   OutputIt d_first,
                                   BinaryOperation binary_op,
                                   UnaryOperation unary_op,

                                   T init );
(since C++17)
(until C++20)
template< class InputIt, class OutputIt,

          class BinaryOperation, class UnaryOperation, class T >
constexpr OutputIt transform_inclusive_scan( InputIt first, InputIt last,
                                             OutputIt d_first,
                                             BinaryOperation binary_op,
                                             UnaryOperation unary_op,

                                             T init );
(since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,

          class BinaryOperation, class UnaryOperation, class T >
ForwardIt2 transform_inclusive_scan( ExecutionPolicy&& policy,
                                     ForwardIt1 first, ForwardIt1 last,
                                     ForwardIt2 d_first,
                                     BinaryOperation binary_op,
                                     UnaryOperation unary_op,

                                     T init );
(4) (since C++17)

Transforms each element in the range [firstlast) with unary_op, then computes an inclusive prefix sum operation using binary_op over the resulting range, optionally with init as the initial value, and writes the results to the range beginning at d_first. Inclusive means that the ith input element is included in the ith sum.

Formally, assigns through each iterator i in [d_firstd_first + (last - first)) the value of

  • for overloads (1,2), the generalized noncommutative sum of unary_op(*j)... for every j in [firstfirst + (i - d_first + 1)) over binary_op,
  • for overloads (3,4), the generalized noncommutative sum of init, unary_op(*j)... for every j in [firstfirst + (i - d_first + 1)) over binary_op,

where generalized noncommutative sum GNSUM(op, a
1
, ..., a
N
)
is defined as follows:

  • if N = 1, a
    1
  • 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.

Overloads (2,4) are executed according to policy. These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

(until C++20)

std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

(since C++20)

unary_op and binary_op shall not invalidate iterators (including the end iterators) or subranges, nor modify elements in the ranges [firstlast) or [d_firstd_first + (last - first)). Otherwise, the behavior is undefined.

Contents

[edit] Parameters

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 if provided
Type requirements
-
InputIt must meet the requirements of LegacyInputIterator.
-
OutputIt must meet the requirements of LegacyOutputIterator.
-
ForwardIt1 must meet the requirements of LegacyForwardIterator.
-
ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
If init is not provided, decltype(first)'s value type must be MoveConstructible and binary_op(unary_op(*first), unary_op(*first)) must be convertible to decltype(first)'s value type.
-
T (if init is provided) 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.

[edit] Return value

Iterator to the element past the last element written.

[edit] Complexity

O(last - first) applications of each of binary_op and unary_op.

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report 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.

[edit] Notes

unary_op is not applied to init.

The parameter init appears last, differing from std::transform_exclusive_scan, because it is optional for this function.

[edit] 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';
}

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

[edit] See also

computes the partial sum of a range of elements
(function template) [edit]
applies a function to a range of elements, storing results in a destination range
(function template) [edit]
similar to std::partial_sum, includes the ith input element in the ith sum
(function template) [edit]
applies an invocable, then calculates exclusive scan
(function template) [edit]