Question

There is a list of items and attribues.

struct Item { double a, b; Item (double a_, double b_): a(a_), b(b_){}};

typedef std::vector <Item> TItems;
typedef std::vector <double> TAttributes;

I am trying to sort items by attributes using a list of pairs:

int main(int argc, char* argv[])
{
    TItems items;
    items.push_back(Item (1.0, 2.0 ));
    items.push_back(Item (3.0, 4.0 ));
    items.push_back(Item (5.0, 6.0 ));

    TAttributes attributes;
    attributes.push_back(8);
    attributes.push_back(7);
    attributes.push_back(9);

    std::pair <TAttributes, TItems> pairs;
    //No element has been coppied
    std::copy (pairs.first.begin(), pairs.first.end(), std::back_inserter (attributes));
     //No element has been coppied
    std::copy (pairs.second.begin(), pairs.second.end(), std::back_inserter (items)); 

    std::sort (pairs.first.begin(), pairs.first.end());
}

There are 2 problems:

A] unsuitable implementation of copying (no ellement has been coppied)

B] too “screwed” code.

Is there any more simple way how to sort list of items using another list of attributes?

How to implement copy operation correctly?

Answer 1

Indeed you are not putting anything in pairs.
See constructor of std::pair.

std::pair <TAttributes, TItems> pairs(attributes_, items_);

Also if you want to reorder Items based on attribute value, you probably want to call std::sort on a list of std::pair<double, Items> (not a pair of list) and provide the appropriate comparison function.