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std::valarray::apply(3)	      C++ Standard Libary      std::valarray::apply(3)

NAME
       std::valarray::apply - std::valarray::apply

Synopsis
	  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 ac-
       quired 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 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.

Possible implementation
	  Following straightforward implementations can	be replaced by expres-
       sion 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 applies a function to a range of elements
	  (C++20)	   (niebloid)

Hidden category:
	    * Pages with unreviewed LWG	DR marker

http://cppreference.com		  2024.06.10	       std::valarray::apply(3)

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