134 lines
4.0 KiB
Markdown
134 lines
4.0 KiB
Markdown
[reduce]
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# 26 Algorithms library [[algorithms]](./#algorithms)
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## 26.10 Generalized numeric operations [[numeric.ops]](numeric.ops#reduce)
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### 26.10.4 Reduce [reduce]
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[ð](#lib:reduce)
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`template<class InputIterator>
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constexpr typename iterator_traits<InputIterator>::value_type
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reduce(InputIterator first, InputIterator last);
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`
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12340)
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*Effects*: Equivalent to:return reduce(first, last, typename iterator_traits<InputIterator>::value_type{});
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[ð](#lib:reduce_)
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`template<class ExecutionPolicy, class ForwardIterator>
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typename iterator_traits<ForwardIterator>::value_type
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reduce(ExecutionPolicy&& exec,
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ForwardIterator first, ForwardIterator last);
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`
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12358)
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*Effects*: Equivalent to:return reduce(std::forward<ExecutionPolicy>(exec), first, last, typename iterator_traits<ForwardIterator>::value_type{});
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[ð](#lib:reduce__)
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`template<class InputIterator, class T>
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constexpr T reduce(InputIterator first, InputIterator last, T init);
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`
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12375)
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*Effects*: Equivalent to:return reduce(first, last, init, plus<>());
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[ð](#lib:reduce___)
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`template<class ExecutionPolicy, class ForwardIterator, class T>
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T reduce(ExecutionPolicy&& exec,
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ForwardIterator first, ForwardIterator last, T init);
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`
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12391)
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*Effects*: Equivalent to:return reduce(std::forward<ExecutionPolicy>(exec), first, last, init, plus<>());
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[ð](#lib:reduce____)
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`template<class InputIterator, class T, class BinaryOperation>
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constexpr T reduce(InputIterator first, InputIterator last, T init,
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BinaryOperation binary_op);
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template<class ExecutionPolicy, class ForwardIterator, class T, class BinaryOperation>
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T reduce(ExecutionPolicy&& exec,
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ForwardIterator first, ForwardIterator last, T init,
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BinaryOperation binary_op);
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`
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12413)
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*Mandates*: All of
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- [(5.1)](#5.1)
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binary_op(init, *first),
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- [(5.2)](#5.2)
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binary_op(*first, init),
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- [(5.3)](#5.3)
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binary_op(init, init), and
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- [(5.4)](#5.4)
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binary_op(*first, *first)
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are convertible to T[.](#5.sentence-1)
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[6](#6)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12424)
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*Preconditions*:
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- [(6.1)](#6.1)
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T meets the [*Cpp17MoveConstructible*](utility.arg.requirements#:Cpp17MoveConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [31](utility.arg.requirements#tab:cpp17.moveconstructible "Table 31: Cpp17MoveConstructible requirements")) requirements[.](#6.1.sentence-1)
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- [(6.2)](#6.2)
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binary_op neither invalidates iterators or subranges,
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nor modifies elements in the range [first, last][.](#6.2.sentence-1)
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[7](#7)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12434)
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*Returns*: *GENERALIZED_SUM*(binary_op, init, *i, …) for every i in [first, last)[.](#7.sentence-1)
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[8](#8)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12439)
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*Complexity*: O(last - first) applications of binary_op[.](#8.sentence-1)
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[9](#9)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L12443)
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[*Note [1](#note-1)*:
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The difference between reduce and accumulate is thatreduce applies binary_op in an unspecified order,
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which yields a nondeterministic result
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for non-associative or non-commutative binary_op such as floating-point addition[.](#9.sentence-1)
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â *end note*]
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