[reduce] (original) (raw)

26 Algorithms library [algorithms]

26.10 Generalized numeric operations [numeric.ops]

26.10.4 Reduce [reduce]

template<class InputIterator> constexpr typename iterator_traits<InputIterator>::value_type reduce(InputIterator first, InputIterator last);

Effects: Equivalent to:return reduce(first, last,typename iterator_traits<InputIterator>::value_type{});

template<class ExecutionPolicy, class ForwardIterator> typename iterator_traits<ForwardIterator>::value_type reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last);

Effects: Equivalent to:return reduce(std::forward<ExecutionPolicy>(exec), first, last,typename iterator_traits<ForwardIterator>::value_type{});

template<class InputIterator, class T> constexpr T reduce(InputIterator first, InputIterator last, T init);

Effects: Equivalent to:return reduce(first, last, init, plus<>());

template<class ExecutionPolicy, class ForwardIterator, class T> T reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, T init);

Effects: Equivalent to:return reduce(std::forward<ExecutionPolicy>(exec), first, last, init, plus<>());

template<class InputIterator, class T, class BinaryOperation> constexpr T reduce(InputIterator first, InputIterator last, T init, BinaryOperation binary_op);template<class ExecutionPolicy, class ForwardIterator, class T, class BinaryOperation> T reduce(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, T init, BinaryOperation binary_op);

Mandates: All of

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

are convertible to T.

Preconditions:

• binary_op neither invalidates iterators or subranges, nor modifies elements in the range [first, last].

Returns: GENERALIZED_SUM(binary_op, init, *i, ...)for every i in [first, last).

Complexity: applications of binary_op.

[Note 1:

The difference between reduce and accumulate is thatreduce applies binary_op in an unspecified order, which yields a nondeterministic result for non-associative or non-commutative binary_opsuch as floating-point addition.

— _end note_]