count.hpp¶

See Public API for a list of names and headers that are part of the public HPX API.

namespace hpx

namespace ranges

Functions

template<typename ExPolicy, typename Rng, typename T, typename Proj = util::projection_identity> util::detail::algorithm_result<ExPolicy, typename std::iterator_traits<typename hpx::traits::range_traits<Rng>::iterator_type>::difference_type>::type count(ExPolicy &&policy, Rng &&rng, T const &value, Proj &&proj = Proj())¶

Returns the number of elements in the range [first, last) satisfying a specific criteria. This version counts the elements that are equal to the given value.

The comparisons in the parallel

count algorithm invoked with an execution policy object of type sequenced_policy execute in sequential order in the calling thread.

Note

Complexity: Performs exactly last - first comparisons.

Template Parameters

ExPolicy: The type of the execution policy to use (deduced). It describes the manner in which the execution of the algorithm may be parallelized and the manner in which it executes the comparisons.
Rng: The type of the source range used (deduced). The iterators extracted from this range type must meet the requirements of an input iterator.
T: The type of the value to search for (deduced).
Proj: The type of an optional projection function. This defaults to util::projection_identity

Parameters

policy: The execution policy to use for the scheduling of the iterations.
rng: Refers to the sequence of elements the algorithm will be applied to.
value: The value to search for.
proj: Specifies the function (or function object) which will be invoked for each of the elements as a projection operation before the actual predicate is invoked.

Note: The comparisons in the parallel count algorithm invoked with an execution policy object of type parallel_policy or parallel_task_policy are permitted to execute in an unordered fashion in unspecified threads, and indeterminately sequenced within each thread.
Return: The count algorithm returns a hpx::future<difference_type> if the execution policy is of type sequenced_task_policy or parallel_task_policy and returns difference_type otherwise (where difference_type is defined by std::iterator_traits<FwdIter>::difference_type. The count algorithm returns the number of elements satisfying the given criteria.

template<typename ExPolicy, typename Rng, typename F, typename Proj = util::projection_identity> util::detail::algorithm_result<ExPolicy, typename std::iterator_traits<typename hpx::traits::range_traits<Rng>::iterator_type>::difference_type>::type count_if(ExPolicy &&policy, Rng &&rng, F &&f, Proj &&proj = Proj())¶

Returns the number of elements in the range [first, last) satisfying a specific criteria. This version counts elements for which predicate f returns true.

Note

Complexity: Performs exactly last - first applications of the predicate.

Note

The assignments in the parallel count_if algorithm invoked with an execution policy object of type sequenced_policy execute in sequential order in the calling thread.

Note

The assignments in the parallel count_if algorithm invoked with an execution policy object of type parallel_policy or parallel_task_policy are permitted to execute in an unordered fashion in unspecified threads, and indeterminately sequenced within each thread.

Return

The count_if algorithm returns hpx::future<difference_type> if the execution policy is of type sequenced_task_policy or parallel_task_policy and returns difference_type otherwise (where difference_type is defined by std::iterator_traits<FwdIter>::difference_type. The count algorithm returns the number of elements satisfying the given criteria.

Template Parameters

ExPolicy: The type of the execution policy to use (deduced). It describes the manner in which the execution of the algorithm may be parallelized and the manner in which it executes the comparisons.
Rng: The type of the source range used (deduced). The iterators extracted from this range type must meet the requirements of an input iterator.
F: The type of the function/function object to use (deduced). Unlike its sequential form, the parallel overload of count_if requires F to meet the requirements of CopyConstructible.
Proj: The type of an optional projection function. This defaults to util::projection_identity

Parameters

policy: The execution policy to use for the scheduling of the iterations.
rng: Refers to the sequence of elements the algorithm will be applied to.
f: Specifies the function (or function object) which will be invoked for each of the elements in the sequence specified by [first, last).This is an unary predicate which returns true for the required elements. The signature of this predicate should be equivalent to:
```
bool pred(const Type &a);
```
The signature does not need to have const&, but the function must not modify the objects passed to it. The type
Type must be such that an object of type FwdIter can be dereferenced and then implicitly converted to Type.
proj: Specifies the function (or function object) which will be invoked for each of the elements as a projection operation before the actual predicate is invoked.