Adding vectors of doubles of differing sizes in C++

Question

I have a number of vector containers of varying size each containing doubles. I would like to add the elements of each vector to create a single vector of doubles. This simple example will example what I'm talking about:

Consider two vectors A with three elements 3.0 2.0 1.0 and B with two elements 2.0 1.0. I would like to add both vectors starting at the last element and working backwards. This would give an array C with entries 3.0 4.0 2.0.

What would be the most elegant/efficent way of doing this?

Thanks!

Answer 1

Once you know you have one vector that is larger than the other

std::vector<double> new_vector = bigger_vector; // Copy the largest
std::transform(smaller_vector.rbegin(), smaller_vector.rend(), // iterate over the complete smaller vector 
    bigger_vector.rbegin(), // 2nd input is the corresponding entries of the larger vector  
    new_vector.rbegin(),    // Output is the new vector 
    std::plus<double>());   // Add em

This is nice because you don't have to do any loop indentation, and works on any sequence container that supports reverse iterators.