Remove Copy with Custom Comparator

std::remove_copy_if() is designed to exclude elements from copying based on a predicate, but it doesn't directly support custom comparators like std::sort() does.

However, you can achieve similar functionality by designing your predicate function to encapsulate your comparison logic.

Here's how you can use std::remove_copy_if() with a custom comparator-like logic within the predicate:

1#include <algorithm>
2#include <iostream>
3#include <vector>
4
5struct Player {
6  std::string Name;
7  int Score;
8};
9
10int main() {
11  std::vector<Player> Players{
12    {"Alice", 10}, {"Bob", 5},
13    {"Charlie", 7}, {"Diana", 2}
14  };
15
16  std::vector<Player> Destination(Players.size());
17
18  // Define the predicate function
19  auto CustomComparator = [](const Player& p) {
20    // Custom logic: exclude players with score < 5
21    return p.Score < 5;
22  };
23
24  // Apply std::remove_copy_if with the predicate
25  auto Result = std::remove_copy_if(
26      Players.begin(), Players.end(),
27      Destination.begin(), CustomComparator);
28
29  // Adjust the size of the destination vector
30  Destination.erase(Result, Destination.end());
31
32  // Display the result
33  std::cout << "Copied players:\n";
34  for (const auto& p : Destination) {
35    std::cout << p.Name << " (Score "
36      << p.Score << ")\n";
37  }
38}

1Copied players:
2Alice (Score 10)
3Bob (Score 5)
4Charlie (Score 7)

In this example:

• We define a predicate CustomComparator to exclude players with a score less than 5.
• We use std::remove_copy_if() to copy elements from the source to the destination, excluding those that meet the condition defined by the predicate.
• After copying, we adjust the size of the destination vector to remove the unused elements.

By embedding the custom comparison logic within the predicate function, you can effectively use std::remove_copy_if() to exclude elements based on complex conditions.

This method is flexible and can be adapted to various types of custom comparisons and conditions, providing a powerful tool for container manipulation in C++.