find_if

Header File: Kokkos_StdAlgorithms.hpp

namespace Kokkos{
namespace Experimental{

template <class ExecutionSpace, class InputIterator, class PredicateType>
InputIterator find_if(const ExecutionSpace& exespace,                                (1)
                      InputIterator first, InputIterator last,
                      PredicateType pred);

template <class ExecutionSpace, class InputIterator, class PredicateType>
InputIterator find_if(const std::string& label, const ExecutionSpace& exespace,      (2)
                      InputIterator first, InputIterator last,
                      PredicateType pred);

template <class ExecutionSpace, class DataType, class... Properties, class PredicateType>
auto find_if(const ExecutionSpace& exespace,
             const Kokkos::View<DataType, Properties...>& view,                      (3)
             PredicateType pred);

template <class ExecutionSpace, class DataType, class... Properties, class PredicateType>
auto find_if(const std::string& label, const ExecutionSpace& exespace,
             const Kokkos::View<DataType, Properties...>& view,                      (4)
             PredicateType pred);

} //end namespace Experimental
} //end namespace Kokkos

Description

Returns an iterator to the first element in [first, last) (1,2) or view (3,4) for which the predicate returns true.

Parameters and Requirements

• exespace, first, last, view: same as in find

• label:

  • for 1, the default string is: “Kokkos::find_if_iterator_api_default”

  • for 3, the default string is: “Kokkos::find_if_view_api_default”

• pred:

  • unary predicate which returns true for the required element; pred(v) must be valid to be called from the execution space passed, and convertible to bool for every argument v of type (possible const) value_type, where value_type is the value type of InputIterator, and must not modify v.

  • must conform to:

  struct Predicate
  {
     KOKKOS_INLINE_FUNCTION
     bool operator()(const /*type needed */ & operand) const { return /* ... */; }
  
     // or, also valid
  
     KOKKOS_INLINE_FUNCTION
     bool operator()(/*type needed */ operand) const { return /* ... */; }
  };
  

Return

• (1,2): InputIterator instance pointing to the first element where the predicate is evaluated to true, or last if no such element is found

• (3,4): iterator to the first element where the predicate is evaluated to true, or Kokkos::Experimental::end(view) if no such element is found

Example

namespace KE = Kokkos::Experimental;

template<class ValueType>
struct EqualsValue
{
  const ValueType m_value;
  EqualsValFunctor(ValueType value) : m_value(value){}

  KOKKOS_INLINE_FUNCTION
  bool operator()(const ValueType & operand) const {
    return operand == m_value;
  }
};

auto exespace = Kokkos::DefaultExecutionSpace;
using view_type = Kokkos::View<exespace, int*>;
view_type a("a", 15);
// fill "a" somehow

// create predicate
EqualsValue<int> p(5);

auto it1 = KE::find_if(exespace, KE::begin(a), KE::end(a), p);

// assuming OpenMP is enabled, then you can also explicitly call
auto it2 = KE::find_if(Kokkos::OpenMP(), KE::begin(a), KE::end(a), p);