Question

Given a vector such as this:

struct product {
    float price;
    float shipping;
};

vector<product> products;

how can I remove all the products from the vector apart from the one with the largest shipping to price ratio?

I tried keeping an iterator to the highest one found so far…

vector<product>::iterator it = products.begin();
vector<product>::iterator largest = products.begin();

while (it != products.end())
{
    if (it->shipping / it->price > largest->shipping / largest->price)
    {
        products.erase(largest);
        largest = it;
        ++it;
    }
    else
    {
        it = products.erase(it);
    }
}

This is all well and good but it fails if the first element in the vector has the highest ratio (it gets deleted). I could get around the problem (I think) if largest was uninitialized and then checking for that in the if statement, but there is no real way of doing this from what I can tell (How to check if the iterator is initialized?).

Any suggestions?

Answer 1

 vector<product> products;
 //populate products

 products.erase(
      products.begin(),
      std::max_element(
          product.begin(), 
          producted.end()
      )
 );
 products.resize(1u);

This assume you have a suitable operator< for your type, if not, make a comparison function and provide it as the third param to max_element.

EDIT:

This work also, in this case, instead of explicitly find the element and delete the element either side, it will sort to find 1 elemnt, then we can do one erase.

 vector<product> products;
 //populate products
 std::nth_element(
      products.begin(), 
      products.begin()+1, 
      products.end(), 
      std::greater<product>()
 );
 products.resize(1u);