std::valarray<T>::apply
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std::valarray
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.
[edit] Parameters
func
-
function to apply to the values
[edit] Return value
The resulting valarray with values acquired by applying function func.
[edit] 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 C++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.
[edit] 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; }
[edit] 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
[edit] See also
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