23 Algorithms library [algorithms]

23.9 Generalized numeric operations [numeric.ops]

23.9.2 Reduce [reduce]

template<class InputIterator> 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> 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> 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);
Requires:
  • T shall be Cpp17MoveConstructible (Table 25).
  • All of binary_­op(init, *first), binary_­op(*first, init), binary_­op(init, init), and binary_­op(*first, *first) shall be convertible to T.
  • binary_­op shall neither invalidate iterators or subranges, nor modify 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
:
The difference between reduce and accumulate is that reduce 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.
end note
]