std::valarray<T>::apply

 

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std::valarray

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valarray::valarray valarray::~valarray valarray::operator= valarray::operator[] valarray::swap valarray::size valarray::resize valarray::sum valarray::min valarray::max valarray::shift valarray::cshift valarray::apply	valarray::operator+valarray::operator-valarray::operator~valarray::operator! valarray::operator+=valarray::operator-=valarray::operator*=valarray::operator/=valarray::operator%=valarray::operator&=valarray::operator|=valarray::operator^=valarray::operator<<=valarray::operator>>=
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swap(std::valarray) (哋它亢++11) begin(std::valarray) (哋它亢++11)   end(std::valarray) (哋它亢++11) abs exp log log10 pow sqrt sin cos tan asin acos atan atan2 sinh cosh tanh	operator*operator/operator%operator+operator-operator^operator&operator|operator<<operator>>operator&&operator|| operator==operator!=operator<operator>operator<=operator>=
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slice_array gslice_array indirect_array	slice gslice mask_array
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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:

• 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.
• For every function taking a const std::valarray<T>& except begin() and end()(since 哋它亢++11), identical functions taking the replacement types shall be added;
• For every function taking two const std::valarray<T>& arguments, identical functions taking every combination of const std::valarray<T>& and replacement types shall be added.
• The return type does not add more than two levels of template nesting over the most deeply-nested argument type.

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.

Run this code

#include <cmath>
#include <iostream>
#include <valarray>
 
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

for_each	applies a function to a range of elements (function template)
ranges::for_each (哋它亢++20)	applies a function to a range of elements (niebloid)