107 lines
7.3 KiB
Markdown
107 lines
7.3 KiB
Markdown
[alg.count]
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# 26 Algorithms library [[algorithms]](./#algorithms)
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## 26.6 Non-modifying sequence operations [[alg.nonmodifying]](alg.nonmodifying#alg.count)
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### 26.6.11 Count [alg.count]
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[ð](#lib:count)
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`template<class InputIterator, class T = iterator_traits<InputIterator>::value_type>
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constexpr typename iterator_traits<InputIterator>::difference_type
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count(InputIterator first, InputIterator last, const T& value);
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template<class ExecutionPolicy, class ForwardIterator,
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class T = iterator_traits<ForwardIterator>::value_type>
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typename iterator_traits<ForwardIterator>::difference_type
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count(ExecutionPolicy&& exec,
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ForwardIterator first, ForwardIterator last, const T& value);
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template<class InputIterator, class Predicate>
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constexpr typename iterator_traits<InputIterator>::difference_type
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count_if(InputIterator first, InputIterator last, Predicate pred);
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template<class ExecutionPolicy, class ForwardIterator, class Predicate>
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typename iterator_traits<ForwardIterator>::difference_type
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count_if(ExecutionPolicy&& exec,
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ForwardIterator first, ForwardIterator last, Predicate pred);
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template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_for [iterator.concept.sentinel]")<I> S, class Proj = identity,
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class T = projected_value_t<I, Proj>>
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requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
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constexpr iter_difference_t<I>
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ranges::count(I first, S last, const T& value, Proj proj = {});
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template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity, class T = projected_value_t<iterator_t<R>, Proj>>
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requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
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constexpr range_difference_t<R>
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ranges::count(R&& r, const T& value, Proj proj = {});
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template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_access_iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_sentinel_for [iterator.concept.sizedsentinel]")<I> S,
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class Proj = identity, class T = projected_value_t<I, Proj>>
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requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
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iter_difference_t<I>
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ranges::count(Ep&& exec, I first, S last, const T& value, Proj proj = {});
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template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
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class T = projected_value_t<iterator_t<R>, Proj>>
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requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to,
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projected<iterator_t<R>, Proj>, const T*>
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range_difference_t<R> ranges::count(Ep&& exec, R&& r, const T& value, Proj proj = {});
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template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_for [iterator.concept.sentinel]")<I> S, class Proj = identity,
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[indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
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constexpr iter_difference_t<I>
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ranges::count_if(I first, S last, Pred pred, Proj proj = {});
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template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
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[indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
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constexpr range_difference_t<R>
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ranges::count_if(R&& r, Pred pred, Proj proj = {});
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template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_access_iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_sentinel_for [iterator.concept.sizedsentinel]")<I> S,
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class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
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iter_difference_t<I>
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ranges::count_if(Ep&& exec, I first, S last, Pred pred, Proj proj = {});
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template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
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[indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
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range_difference_t<R>
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ranges::count_if(Ep&& exec, R&& r, Pred pred, Proj proj = {});
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`
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5436)
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Let E be:
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- [(1.1)](#1.1)
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*i == value for the overloads
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with no parameter pred or proj;
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- [(1.2)](#1.2)
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pred(*i) != false for the overloads
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with a parameter pred but no parameter proj;
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- [(1.3)](#1.3)
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invoke(proj, *i) == value for the overloads
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with a parameter proj but no parameter pred;
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- [(1.4)](#1.4)
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bool(invoke(pred, invoke(proj, *i))) for the overloads
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with both parameters proj and pred[.](#1.sentence-1)
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5453)
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*Effects*: Returns the number of iterators i in the range [first, last)
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for which E holds[.](#2.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5458)
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*Complexity*: Exactly last - first applications
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of the corresponding predicate and any projection[.](#3.sentence-1)
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