Question

I have

    vector<vector<int>> vec 

in my c++ app.

Every vector of integers as an element of “big” vector has 4 INT values.
I want to sort vec basing on third value of it’s content vectors of ints (I mean every “inside” vector third element) – is it possible?

EDIT

Let’s say I’ve got a function

COST(vector<int>)

which calculates me some value based on my vector values – can I use it in comparation parameter too? It’d help me a lot more.

Answer 1

Sure it is. std::sort can take a third parameter which is the comparison function to use when sorting. For example, you could use a lambda function:

std::vector<std::vector<int>> vec;
// Fill it

std::sort(vec.begin(), vec.end(),
          [](const std::vector<int>& a, const std::vector<int>& b) {
  return a[2] < b[2];
});

Alternatively, you can pass anything else callable with signature bool(const std::vector<int>&, const std::vector<int>&), such as a functor or function pointer.

---

Response to edit: Simply apply your COST function to a and b:

std::sort(vec.begin(), vec.end(),
          [](const std::vector<int>& a, const std::vector<int>& b) {
  return COST(a) < COST(b);
});