Removal Algorithms

Remove Copy with Custom Comparator

Is there a way to use remove_copy_if() with a custom comparator function?

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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:

#include <algorithm>
#include <iostream>
#include <vector>

struct Player {
  std::string Name;
  int Score;

int main() {
  std::vector<Player> Players{
    {"Alice", 10}, {"Bob", 5},
    {"Charlie", 7}, {"Diana", 2}

  std::vector<Player> Destination(Players.size());

  // Define the predicate function
  auto CustomComparator = [](const Player& p) {
    // Custom logic: exclude players with score < 5
    return p.Score < 5;

  // Apply std::remove_copy_if with the predicate
  auto Result = std::remove_copy_if(
      Players.begin(), Players.end(),
      Destination.begin(), CustomComparator);

  // Adjust the size of the destination vector
  Destination.erase(Result, Destination.end());

  // Display the result
  std::cout << "Copied players:\n";
  for (const auto& p : Destination) {
    std::cout << p.Name << " (Score "
      << p.Score << ")\n";
Copied players:
Alice (Score 10)
Bob (Score 5)
Charlie (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++.

Answers to questions are automatically generated and may not have been reviewed.

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