Question

Could someone help me to write a logic that converts a ID array to a 2D vector.

something like

int array[] = {1, 4, 5, 7, 9, 3}; // dynamic array
vector <vector int> ex;

How can I now place the values in ex from array.. so that it forms 2 vectors each of 3 values?

I have searched for help with no use and have tried it myself as below:

for(int i=0; i<2; i++)
{   
        rowTemp_ex.assign(array, array+3));
 ex.push_back(rowTemp_ex);
 rowTemp_ex.erase(rowTemp_ex.begin() , rowTemp_ex.end());
}

Answer 1

First, compute how many row-vectors there will be. If each one has three elements, the total is the size of the array divided by 3.

template <typename T, std::size_t N>
std::size_t size(T(&)[N]) { return N; }

int number_of_rows = size(array) / 3;

Now create a vector with that number of row-vectors with three elements each:

std::vector<std::vector<int> > v(number_of_rows, std::vector<int>(3));

And then go through the original array and fill up each cell of the result, using integer division and remainder operations:

for(int i = 0; i < size(array); ++i) {
    v[i / 3][i % 3] = array[i];
}