transform

Prototype

template<class F, class... R>
auto transform(F f, R... rasters)

template<class F, class... R>
auto transform(std::reference_wrapper<F> f, R... rasters)

Description

Create a non-mutable RasterView that applies the Callable f cell-by-cell to the corresponding elements in rasters. The Callable cannot modify its input variables. The first prototype copies f by value, the second takes a reference.

Definition

<pronto/raster/transform_raster_view.h> (open in Github)

Requirements on types

F is a callable that takes as many input arguments as the are input rasters. The type of the input arguments must correspond to the value_type of the respective rasters. F must be copy-constructible, or be wrapped in a std::reference_wrapper.

Preconditions

All rasters must have the same dimensions. The Callable f is passed by value and should therefore be copy-constructible at negligible cost.

Complexity

O(1)

Example of use

//example_transform.cpp

#include <pronto/raster/io.h>
#include <pronto/raster/plot_raster.h>
#include <pronto/raster/transform_raster_view.h>

namespace pr = pronto::raster;

template<class T>
T join(const T& a, const T& b, const T& c)
{
  return 100 * a + 10 * b + c;
}

struct sum
{
  template<class T>
  T operator()(const T& a, const T& b, const T& c) 
  {
    return a + b + c;
  }
};

int main()
{
  auto product = [](int a, int b, int c) { return a * b * c;  };
  
  auto aa = pr::create_temp<int>(4, 5);
  auto bb = pr::create_temp<int>(4, 5);
  auto cc = pr::create_temp<int>(4, 5);
  int i = 0;
  for (auto&& v : aa) {
    v = ((i += 3) %= 7);
  }

  for (auto&& v : bb) {
    v = ((i += 3) %= 7);
  }

  for (auto&& v : cc) {
    v = ((i += 3) %= 7);
  }

  auto join_abc = pr::transform(join<int>, aa, bb, cc);
  auto sum_abc = pr::transform(sum{}, aa, bb, cc);
  auto product_abc = pr::transform(product, aa, bb, cc);

  plot_raster(join_abc);
  plot_raster(sum_abc);
  plot_raster(product_abc);

  return 0;
}

Output:

Rows: 4, Cols: 5, Value type: int
304     630     263     526     152
415     41      304     630     263
526     152     415     41      304
630     263     526     152     415

Rows: 4, Cols: 5, Value type: int
7       9       11      13      8
10      5       7       9       11
13      8       10      5       7
9       11      13      8       10

Rows: 4, Cols: 5, Value type: int
0       0       36      60      10
20      0       0       0       36
60      10      20      0       0
0       36      60      10      20

Notes

The return type of the transform function is considered to be an implementation detail and can change in future. However, it will always be a model of RasterView.

See also