How to filter object in c++ [duplicate]

Question

Let's say I have a class:

class Cell {
  int ID;
  int valueX;
  int valueY;
};

and in main() I declared vector of Cells:

vector<Cell> myCells;

My problem is to write a function that gets vector of Cells, operator (gt - greater than, le - less or equal, and so on), name of a variable and an integer, and returns vector of Cells that meets the requirement? For example:

vector<Cells> resultCells = filter(myCells, gt, valueX, 5)

is vector of Cells where each cell has valueX greater than 5.

My first attempts required a lot of ifs and switches and I'm sure it's not proper solution. Then I asked a friend for a tip, he told me about things like functors, lambdas, std::function, std::map, std::bind, that can help me to do this and I've read about it but I am unable to use in in practise.

One of examples that I've seen on the Internet is this one, but it's less complex and hard to reuse (for me).

Answer 1

Try something like this using std::copy_if :

std::vector<Cell> resultCells;
std::copy_if(myCells.begin(), myCells.end(),
             std::back_inserter(resultCells),
             [](const Cell& c) { return c.valueX > 5; });