std::transform_inclusive_scan (3) - Linux Man Pages

std::transform_inclusive_scan: std::transform_inclusive_scan

NAME

std::transform_inclusive_scan - std::transform_inclusive_scan

Synopsis


Defined in header <numeric>
template< class InputIt, class OutputIt,
class BinaryOperation, class UnaryOperation > (1) (since C++17)
OutputIt transform_inclusive_scan( InputIt first, InputIt last, OutputIt d_first,
BinaryOperation binary_op, UnaryOperation unary_op );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
class BinaryOperation, class UnaryOperation >
ForwardIt2 transform_inclusive_scan( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first,
BinaryOperation binary_op, UnaryOperation unary_op );
template< class InputIt, class OutputIt,
class BinaryOperation, class UnaryOperation, class T >
OutputIt transform_inclusive_scan( InputIt first, InputIt last, OutputIt d_first, (3) (since C++17)
BinaryOperation binary_op, UnaryOperation unary_op,
T init );
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2,
class BinaryOperation, class UnaryOperation, class T >
ForwardIt2 transform_inclusive_scan( ExecutionPolicy&& policy, (4) (since C++17)
ForwardIt1 first, ForwardIt1 last, ForwardIt2 d_first,
BinaryOperation binary_op, UnaryOperation unary_op,
T init );


Transforms each element in the range [first, last) 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 i-th input element is included in the i-th sum.
Formally, assigns through each iterator i in [d_first, d_first + (last - first)) the value of


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

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. and, if init is not provided, ForwardIt1's value_type must be MoveConstructible and binary_op(unary_op(*first), unary_op(*first)) must be convertible to ForwardIt1's value type
-
ForwardIt2 must meet the requirements of LegacyForwardIterator.
-
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

Return value


Iterator to the element past the last element written.

Complexity


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

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.

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.

Example


// 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);

  }

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

See also


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


inclusive_scan similar to std::partial_sum, includes the ith input element in the ith sum
                         (function template)
(C++17)


transform_exclusive_scan applies a functor, then calculates exclusive scan
                         (function template)
(C++17)