How to split a vector into n “almost equal” parts

Question

I have a problem that I would like to merge a large number of images using ImageMagick\'s convert.exe, but under Windows I have a 8192 byte long command line limit.

Answer 1

You could create a template that returns a std::vector < std::vector > and receives the vector you want split, and the number of divisions. using for and iterator is very easy.

#include 
#include 
#include 
#include 
#include 

template
std::vector< std::vector > split(std::vector vec, uint64_t n) {
  std::vector< std::vector > vec_of_vecs(n);

  uint64_t quotient = vec.size() / n;
  uint64_t reminder = vec.size() % n;
  uint64_t first = 0;
  uint64_t last;
  for (uint64_t i = 0; i < n; ++i) {
    if (i < reminder) {
      last = first + quotient + 1;
      vec_of_vecs[i] = std::vector(vec.begin() + first, vec.begin() + last);
      first = last;
  }
    else if (i != n - 1) {
    last = first +  quotient;
    vec_of_vecs[i] = std::vector(vec.begin() + first, vec.begin() + last);
    first = last;
  }
    else
    vec_of_vecs[i] = std::vector(vec.begin() + first, vec.end());
}

return vec_of_vecs;
}

#define ONE_DIMENSION 11
#define SPLITS 3

int main(void)
{
  std::vector vector(ONE_DIMENSION);
  std::iota(std::begin(vector), std::end(vector), 1);

  std::vector> vecs(SPLITS);
  vecs = split(vector, SPLITS);

  for (uint64_t m = 0; m < vecs.size(); ++m) {
    for (auto i : vecs[m])
      std::cout << std::setw(3) << i << " ";
    std::cout << std::endl;
  }


  return 0;
}