Copy selected values (via view) from boost::multi_array to another array (C++)

Question

How can I copy (deep-copy) a selcted range (view) from a boost::multi_array to another array?

Answer 1

The values can be copied via =operator.

#include <iostream>
#include <string>
#include <boost/multi_array.hpp>

template<typename T>
void initArray(T& to_initialize)
{
  int value = 0;
  for(size_t i=0;i<to_initialize.shape()[0];++i){
      for(size_t j=0;j<to_initialize.shape()[1];++j){
          to_initialize[i][j]=value;
          ++value;
      }
  }
}

template<typename T>
void printArray(T& to_print, std::string additional_text)
{
    std::cout<<"**************"<<additional_text<<"*****************"<<std::endl;
    for(size_t i=0;i<to_print.shape()[0];++i){
      for(size_t j=0;j<to_print.shape()[1];++j){
         std::cout<<to_print[i][j]<<", ";
      }
      std::cout<<std::endl;
    }
    std::cout<<"*******************************"<<std::endl;
}

int main()
{
  auto big_array = boost::multi_array<double, 2>(boost::extents[10][10]);
  initArray(big_array);
  printArray(big_array, "initial big array");
  
  using range = boost::multi_array_types::index_range;
  boost::multi_array<double, 2>::index_gen indices;
  boost::multi_array<double, 2>::array_view<2>::type big_array_view = big_array[ indices[range(0,2)][range(0,4)] ];
  
  auto small_array = boost::multi_array<double, 2>(boost::extents[2][4]);
  small_array = big_array_view; //Deep Copy
  
  printArray(small_array, "small array after copy");
  
  big_array_view[0][0]=999; // Does not affect small_array
  printArray(big_array,  "big array after modifying"); 
  printArray(small_array, "small array is not affected after modifying big array");
}

Output is:

**************initial big array*****************
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 
20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 
30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 
40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 
50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 
60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 
70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 
80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 
90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 
*******************************
**************small array after copy*****************
0, 1, 2, 3, 
10, 11, 12, 13, 
*******************************
**************big array after modifying*****************
999, 1, 2, 3, 4, 5, 6, 7, 8, 9, 
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 
20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 
30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 
40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 
50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 
60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 
70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 
80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 
90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 
*******************************
**************small array is not affected after modifying big array*****************
0, 1, 2, 3, 
10, 11, 12, 13, 
*******************************