copy 2d vector without first row and column

Question

Just like in topic. I would like to copy one vector to another without first row and column.

'''

std::vector<std::vector<int>> v2(v1.size()-1,std::vector<int>(v1.size()-1));

std::copy((v1.begin()+1)->begin()+1,v1.end()->end(),v2.begin()->begin());

return v2;

'''

Answer 1

Using C++ and views it is easy to drop items while enumerating. So you can avoid using raw or iterator loops. Live demo here : https://godbolt.org/z/8xz91Y8cK

#include <ranges>
#include <iostream>
#include <vector>

auto reduce_copy(const std::vector<std::vector<int>> values)
{
    std::vector<std::vector<int>> retval{};

    // drop first row
    for (const auto& row : values | std::views::drop(1))
    {
        // add a new row to retval
        auto& new_row = retval.emplace_back();

        // drop first column
        for (const auto& col : row | std::views::drop(1))
        {
            new_row.emplace_back(col);
        }
    }

    return retval;
}


int main()
{

    std::vector<std::vector<int>> values{ {1,2,3}, {4,5,6}, {7,8,9} };
    auto result = reduce_copy(values);

    for (const auto& row : result)
    {
        for (const auto& value : row)
        {
            std::cout << value << " ";
        }
        std::cout << "\n";
    }
    
    
    return 0;
}