std::valarray<T>::apply

valarray<T> apply( T func(T) ) const;

valarray<T> apply( T func(const T&) ) const;

Returns a new valarray of the same size with values which are acquired by applying function func to the previous values of the elements.

Parameters

Return value

The resulting valarray with values acquired by applying function func.

Notes

The function can be implemented with the return type different from std::valarray. In this case, the replacement type has the following properties:

• All const member functions of std::valarray are provided.
• std::valarray, std::slice_array, std::gslice_array, std::mask_array and std::indirect_array can be constructed from the replacement type.
• All functions accepting an argument of type const std::valarray& except begin() and end() (since C++11) should also accept the replacement type.
• All functions accepting two arguments of type const std::valarray& should accept every combination of const std::valarray& and the replacement type.
• The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

Possible implementation

Following silly implementations can be replaced by expression templates for a higher efficiency.

template<class T>
valarray<T> valarray<T>::apply( T func(T) ) const
{
    valarray<T> other = *this;
    for (T &i : other) {
        i = func(i);
    }
    return other;
}
 
template<class T>
valarray<T> valarray<T>::apply( T func(const T&) ) const
{
    valarray<T> other = *this;
    for (T &i : other) {
        i = func(i);
    }
    return other;
}

Example

#include <iostream>
#include <valarray>
#include <cmath>
 
int main()
{
    std::valarray<int> v = {1,2,3,4,5,6,7,8,9,10};
    v = v.apply([](int n)->int {
                    return std::round(std::tgamma(n+1));
                });
    for(auto n : v) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
}

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See also