4.0 KiB
[reduce]
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::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(exec), first, last, typename iterator_traits::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(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:
-
T meets the Cpp17MoveConstructible (Table 31) requirements.
-
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: O(last - first) 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_op such as floating-point addition.
â end note]