Filter

Include <mln/core/ranges/view/filter.hpp>

template<class Pred>
auto view::filter(Range r, Pred fun)

Parameters:

• r – Input range

• fun – Predicate to apply on each element

filter returns a view of the input range with elements that satisfies the predicate fun i.e. \(\{v \in \mathcal{R} \mid fun(v)\}\). This view preserves the following properties:

Properties	r	filter(r, fun)
Segmented	X	X
Forward	X	X
Reversible	X	X
Bidirectional	X	X
Random Access	X	X
Contiguous	X
Writable	X	X

Examples

• Only white squares of a chessboard:

  box2d box = {{0,0}, {3,4}};
  auto is_white = [](point2d p) { return (p[0] % 2) == (p[1] % 2); };
  mln_foreach(auto p, ranges::view::filter(box, is_white))
    std::cout << p << ",";
  

  Outputs:

  (0,0),(0,2),(1,1),(1,3),(2,0),(2,2),
  

• Set pair numbers to 0:

   std::vector<int> v = {0, 1, 2, 3, 4, 5, 6};
   auto is_pair = [](int x) { return x % 2 == 0; };
   mln_foreach(auto&& n, ranges::view::filter(v, is_pair))
     v = 0;
  
  for(const auto& e : v)
    std::cout << e << ", ";
  

  Outputs:

  0, 1, 0, 3, 0, 5, 0,