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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

func - function to apply to the values

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:

Possible implementation

Following straightforward 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

calculates and prints the first 10 factorials.

#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';
}

Output:

1 2 6 24 120 720 5040 40320 362880 3628800

See also

applies a function to a range of elements
(function template)
(C++20)
applies a function to a range of elements
(niebloid)

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